Migrate tests to null-safety (#67692)

packages/flutter/test/material/text_theme_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -52,7 +50,7 @@ void main() {
   test('TextTheme merges properly in the presence of null fields.', () {
     const TextTheme partialTheme = TextTheme(headline6: TextStyle(color: Color(0xcafefeed)));
     final TextTheme fullTheme = ThemeData.fallback().textTheme.merge(partialTheme);
-    expect(fullTheme.headline6.color, equals(partialTheme.headline6.color));
+    expect(fullTheme.headline6!.color, equals(partialTheme.headline6!.color));
 
     const TextTheme onlyHeadlineAndTitle = TextTheme(
       headline5: TextStyle(color: Color(0xcafefeed)),
@@ -64,9 +62,9 @@ void main() {
     );
     TextTheme merged = onlyHeadlineAndTitle.merge(onlyBody1AndTitle);
     expect(merged.bodyText1, isNull);
-    expect(merged.bodyText2.color, equals(onlyBody1AndTitle.bodyText2.color));
-    expect(merged.headline5.color, equals(onlyHeadlineAndTitle.headline5.color));
-    expect(merged.headline6.color, equals(onlyBody1AndTitle.headline6.color));
+    expect(merged.bodyText2!.color, equals(onlyBody1AndTitle.bodyText2!.color));
+    expect(merged.headline5!.color, equals(onlyHeadlineAndTitle.headline5!.color));
+    expect(merged.headline6!.color, equals(onlyBody1AndTitle.headline6!.color));
 
     merged = onlyHeadlineAndTitle.merge(null);
     expect(merged, equals(onlyHeadlineAndTitle));
@@ -96,34 +94,34 @@ void main() {
       decorationStyle: decorationStyle,
     );
 
-    expect(theme.headline1.color, displayColor);
-    expect(theme.headline2.color, displayColor);
-    expect(theme.headline3.color, displayColor);
-    expect(theme.headline4.color, displayColor);
-    expect(theme.caption.color, displayColor);
-    expect(theme.headline5.color, bodyColor);
-    expect(theme.headline6.color, bodyColor);
-    expect(theme.subtitle1.color, bodyColor);
-    expect(theme.bodyText1.color, bodyColor);
-    expect(theme.bodyText2.color, bodyColor);
-    expect(theme.button.color, bodyColor);
-    expect(theme.subtitle2.color, bodyColor);
-    expect(theme.overline.color, bodyColor);
+    expect(theme.headline1!.color, displayColor);
+    expect(theme.headline2!.color, displayColor);
+    expect(theme.headline3!.color, displayColor);
+    expect(theme.headline4!.color, displayColor);
+    expect(theme.caption!.color, displayColor);
+    expect(theme.headline5!.color, bodyColor);
+    expect(theme.headline6!.color, bodyColor);
+    expect(theme.subtitle1!.color, bodyColor);
+    expect(theme.bodyText1!.color, bodyColor);
+    expect(theme.bodyText2!.color, bodyColor);
+    expect(theme.button!.color, bodyColor);
+    expect(theme.subtitle2!.color, bodyColor);
+    expect(theme.overline!.color, bodyColor);
 
     final List<TextStyle> themeStyles = <TextStyle>[
-      theme.headline1,
-      theme.headline2,
-      theme.headline3,
-      theme.headline4,
-      theme.caption,
-      theme.headline5,
-      theme.headline6,
-      theme.subtitle1,
-      theme.bodyText1,
-      theme.bodyText2,
-      theme.button,
-      theme.subtitle2,
-      theme.overline,
+      theme.headline1!,
+      theme.headline2!,
+      theme.headline3!,
+      theme.headline4!,
+      theme.caption!,
+      theme.headline5!,
+      theme.headline6!,
+      theme.subtitle1!,
+      theme.bodyText1!,
+      theme.bodyText2!,
+      theme.button!,
+      theme.subtitle2!,
+      theme.overline!,
     ];
     expect(themeStyles.every((TextStyle style) => style.fontFamily == fontFamily), true);
     expect(themeStyles.every((TextStyle style) => style.decorationColor == decorationColor), true);
@@ -139,19 +137,19 @@ void main() {
       fontSizeDelta: 5.0,
     );
 
-    expect(sizeTheme.headline1.fontSize, baseTheme.headline1.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.headline2.fontSize, baseTheme.headline2.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.headline3.fontSize, baseTheme.headline3.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.headline4.fontSize, baseTheme.headline4.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.caption.fontSize, baseTheme.caption.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.headline5.fontSize, baseTheme.headline5.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.headline6.fontSize, baseTheme.headline6.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.subtitle1.fontSize, baseTheme.subtitle1.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.bodyText1.fontSize, baseTheme.bodyText1.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.bodyText2.fontSize, baseTheme.bodyText2.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.button.fontSize, baseTheme.button.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.subtitle2.fontSize, baseTheme.subtitle2.fontSize * 2.0 + 5.0);
-    expect(sizeTheme.overline.fontSize, baseTheme.overline.fontSize * 2.0 + 5.0);
+    expect(sizeTheme.headline1!.fontSize, baseTheme.headline1!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.headline2!.fontSize, baseTheme.headline2!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.headline3!.fontSize, baseTheme.headline3!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.headline4!.fontSize, baseTheme.headline4!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.caption!.fontSize, baseTheme.caption!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.headline5!.fontSize, baseTheme.headline5!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.headline6!.fontSize, baseTheme.headline6!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.subtitle1!.fontSize, baseTheme.subtitle1!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.bodyText1!.fontSize, baseTheme.bodyText1!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.bodyText2!.fontSize, baseTheme.bodyText2!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.button!.fontSize, baseTheme.button!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.subtitle2!.fontSize, baseTheme.subtitle2!.fontSize! * 2.0 + 5.0);
+    expect(sizeTheme.overline!.fontSize, baseTheme.overline!.fontSize! * 2.0 + 5.0);
   });
 
   test('TextTheme lerp with second parameter null', () {

packages/flutter/test/material/theme_data_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -37,8 +35,8 @@ void main() {
     final ThemeData darkTheme = ThemeData(brightness: Brightness.dark);
     final Typography typography = Typography.material2018(platform: lightTheme.platform);
 
-    expect(lightTheme.textTheme.headline6.color, typography.black.headline6.color);
-    expect(darkTheme.textTheme.headline6.color, typography.white.headline6.color);
+    expect(lightTheme.textTheme.headline6!.color, typography.black.headline6!.color);
+    expect(darkTheme.textTheme.headline6!.color, typography.white.headline6!.color);
   });
 
   test('Default primary text theme contrasts with primary brightness', () {
@@ -46,8 +44,8 @@ void main() {
     final ThemeData darkTheme = ThemeData(primaryColorBrightness: Brightness.dark);
     final Typography typography = Typography.material2018(platform: lightTheme.platform);
 
-    expect(lightTheme.primaryTextTheme.headline6.color, typography.black.headline6.color);
-    expect(darkTheme.primaryTextTheme.headline6.color, typography.white.headline6.color);
+    expect(lightTheme.primaryTextTheme.headline6!.color, typography.black.headline6!.color);
+    expect(darkTheme.primaryTextTheme.headline6!.color, typography.white.headline6!.color);
   });
 
   test('Default accent text theme contrasts with accent brightness', () {
@@ -55,8 +53,8 @@ void main() {
     final ThemeData darkTheme = ThemeData(accentColorBrightness: Brightness.dark);
     final Typography typography = Typography.material2018(platform: lightTheme.platform);
 
-    expect(lightTheme.accentTextTheme.headline6.color, typography.black.headline6.color);
-    expect(darkTheme.accentTextTheme.headline6.color, typography.white.headline6.color);
+    expect(lightTheme.accentTextTheme.headline6!.color, typography.black.headline6!.color);
+    expect(darkTheme.accentTextTheme.headline6!.color, typography.white.headline6!.color);
   });
 
   test('Default chip label style gets a default bodyText1 if textTheme.bodyText1 is null', () {
@@ -65,8 +63,8 @@ void main() {
     final ThemeData darkTheme = ThemeData(brightness: Brightness.dark, textTheme: noBodyText1TextTheme);
     final Typography typography = Typography.material2018(platform: lightTheme.platform);
 
-    expect(lightTheme.chipTheme.labelStyle.color, equals(typography.black.bodyText1.color.withAlpha(0xde)));
-    expect(darkTheme.chipTheme.labelStyle.color, equals(typography.white.bodyText1.color.withAlpha(0xde)));
+    expect(lightTheme.chipTheme.labelStyle.color, equals(typography.black.bodyText1!.color!.withAlpha(0xde)));
+    expect(darkTheme.chipTheme.labelStyle.color, equals(typography.white.bodyText1!.color!.withAlpha(0xde)));
   });
 
   test('Default icon theme contrasts with brightness', () {
@@ -74,8 +72,8 @@ void main() {
     final ThemeData darkTheme = ThemeData(brightness: Brightness.dark);
     final Typography typography = Typography.material2018(platform: lightTheme.platform);
 
-    expect(lightTheme.textTheme.headline6.color, typography.black.headline6.color);
-    expect(darkTheme.textTheme.headline6.color, typography.white.headline6.color);
+    expect(lightTheme.textTheme.headline6!.color, typography.black.headline6!.color);
+    expect(darkTheme.textTheme.headline6!.color, typography.white.headline6!.color);
   });
 
   test('Default primary icon theme contrasts with primary brightness', () {
@@ -83,8 +81,8 @@ void main() {
     final ThemeData darkTheme = ThemeData(primaryColorBrightness: Brightness.dark);
     final Typography typography = Typography.material2018(platform: lightTheme.platform);
 
-    expect(lightTheme.primaryTextTheme.headline6.color, typography.black.headline6.color);
-    expect(darkTheme.primaryTextTheme.headline6.color, typography.white.headline6.color);
+    expect(lightTheme.primaryTextTheme.headline6!.color, typography.black.headline6!.color);
+    expect(darkTheme.primaryTextTheme.headline6!.color, typography.white.headline6!.color);
   });
 
   test('Default accent icon theme contrasts with accent brightness', () {
@@ -92,8 +90,8 @@ void main() {
     final ThemeData darkTheme = ThemeData(accentColorBrightness: Brightness.dark);
     final Typography typography = Typography.material2018(platform: lightTheme.platform);
 
-    expect(lightTheme.accentTextTheme.headline6.color, typography.black.headline6.color);
-    expect(darkTheme.accentTextTheme.headline6.color, typography.white.headline6.color);
+    expect(lightTheme.accentTextTheme.headline6!.color, typography.black.headline6!.color);
+    expect(darkTheme.accentTextTheme.headline6!.color, typography.white.headline6!.color);
   });
 
   testWidgets('Defaults to MaterialTapTargetBehavior.padded on mobile platforms and MaterialTapTargetBehavior.shrinkWrap on desktop', (WidgetTester tester) async {
@@ -120,12 +118,12 @@ void main() {
       ),
     );
 
-    expect(themeData.textTheme.bodyText1.fontFamily, equals('Ahem'));
-    expect(themeData.primaryTextTheme.headline3.fontFamily, equals('Ahem'));
-    expect(themeData.accentTextTheme.headline1.fontFamily, equals('Ahem'));
+    expect(themeData.textTheme.bodyText1!.fontFamily, equals('Ahem'));
+    expect(themeData.primaryTextTheme.headline3!.fontFamily, equals('Ahem'));
+    expect(themeData.accentTextTheme.headline1!.fontFamily, equals('Ahem'));
 
     // Shouldn't override the specified style's family
-    expect(themeData.textTheme.headline6.fontFamily, equals('Roboto'));
+    expect(themeData.textTheme.headline6!.fontFamily, equals('Roboto'));
   });
 
   test('Can estimate brightness - directly', () {
@@ -192,7 +190,7 @@ void main() {
   });
 
   testWidgets('VisualDensity.adaptivePlatformDensity returns adaptive values', (WidgetTester tester) async {
-    switch (debugDefaultTargetPlatformOverride) {
+    switch (debugDefaultTargetPlatformOverride!) {
       case TargetPlatform.android:
       case TargetPlatform.iOS:
       case TargetPlatform.fuchsia:
@@ -207,7 +205,7 @@ void main() {
 
   testWidgets('VisualDensity in ThemeData defaults to "compact" on desktop and "standard" on mobile', (WidgetTester tester) async {
     final ThemeData themeData = ThemeData();
-    switch (debugDefaultTargetPlatformOverride) {
+    switch (debugDefaultTargetPlatformOverride!) {
       case TargetPlatform.android:
       case TargetPlatform.iOS:
       case TargetPlatform.fuchsia:

packages/flutter/test/material/theme_defaults_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -28,7 +26,7 @@ void main() {
       );
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
-      expect(raw.textStyle.color, const Color(0xdd000000));
+      expect(raw.textStyle!.color, const Color(0xdd000000));
       expect(raw.fillColor, const Color(0xffe0e0e0));
       expect(raw.highlightColor, const Color(0x29000000)); // Was Color(0x66bcbcbc)
       expect(raw.splashColor, const Color(0x1f000000)); // Was Color(0x66c8c8c8)
@@ -56,7 +54,7 @@ void main() {
       );
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
-      expect(raw.textStyle.color, const Color(0x61000000));
+      expect(raw.textStyle!.color, const Color(0x61000000));
       expect(raw.fillColor, const Color(0x61000000));
       // highlightColor, disabled button can't be pressed
       // splashColor, disabled button doesn't splash
@@ -86,7 +84,7 @@ void main() {
       );
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
-      expect(raw.textStyle.color, const Color(0xdd000000));
+      expect(raw.textStyle!.color, const Color(0xdd000000));
       expect(raw.fillColor, null);
       expect(raw.highlightColor, const Color(0x29000000)); // Was Color(0x66bcbcbc)
       expect(raw.splashColor, const Color(0x1f000000)); // Was Color(0x66c8c8c8)
@@ -114,7 +112,7 @@ void main() {
       );
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
-      expect(raw.textStyle.color, const Color(0x61000000));
+      expect(raw.textStyle!.color, const Color(0x61000000));
       expect(raw.fillColor, null);
       // highlightColor, disabled button can't be pressed
       // splashColor, disabled button doesn't splash
@@ -148,7 +146,7 @@ void main() {
       );
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
-      expect(raw.textStyle.color, const Color(0xdd000000));
+      expect(raw.textStyle!.color, const Color(0xdd000000));
       expect(raw.fillColor, const Color(0x00fafafa));
       expect(raw.highlightColor, const Color(0x29000000)); // Was Color(0x66bcbcbc)
       expect(raw.splashColor, const Color(0x1f000000)); // Was Color(0x66c8c8c8)
@@ -175,7 +173,7 @@ void main() {
       );
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
-      expect(raw.textStyle.color, const Color(0xdd000000));
+      expect(raw.textStyle!.color, const Color(0xdd000000));
       expect(raw.fillColor, Colors.transparent);
       expect(raw.highlightColor, const Color(0x29000000)); // Was Color(0x66bcbcbc)
       expect(raw.splashColor, const Color(0x1f000000)); // Was Color(0x66c8c8c8)
@@ -202,7 +200,7 @@ void main() {
       );
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
-      expect(raw.textStyle.color, const Color(0x61000000));
+      expect(raw.textStyle!.color, const Color(0x61000000));
       expect(raw.fillColor, const Color(0x00000000));
       // highlightColor, disabled button can't be pressed
       // splashColor, disabled button doesn't splash
@@ -236,7 +234,7 @@ void main() {
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
       expect(raw.enabled, true);
-      expect(raw.textStyle.color, const Color(0xffffffff));
+      expect(raw.textStyle!.color, const Color(0xffffffff));
       expect(raw.fillColor, const Color(0xff2196f3));
       expect(raw.elevation, 6.0);
       expect(raw.highlightElevation, 12.0);
@@ -263,7 +261,7 @@ void main() {
 
       final RawMaterialButton raw = tester.widget<RawMaterialButton>(find.byType(RawMaterialButton));
       expect(raw.enabled, false);
-      expect(raw.textStyle.color, const Color(0xffffffff));
+      expect(raw.textStyle!.color, const Color(0xffffffff));
       expect(raw.fillColor, const Color(0xff2196f3));
       // highlightColor, disabled button can't be pressed
       // splashColor, disabled button doesn't splash

packages/flutter/test/material/theme_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:ui' as ui;
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
@@ -46,11 +44,11 @@ void main() {
     await tester.tap(find.byKey(popupMenuButtonKey));
     await tester.pump(const Duration(seconds: 1));
 
-    expect(Theme.of(tester.element(find.text('menuItem'))).brightness, equals(Brightness.dark));
+    expect(Theme.of(tester.element(find.text('menuItem')))!.brightness, equals(Brightness.dark));
   });
 
   testWidgets('Fallback theme', (WidgetTester tester) async {
-    BuildContext capturedContext;
+    late BuildContext capturedContext;
     await tester.pumpWidget(
       Builder(
         builder: (BuildContext context) {
@@ -116,7 +114,7 @@ void main() {
     await tester.tap(find.byKey(popupMenuButtonKey));
     await tester.pump(const Duration(seconds: 1));
 
-    expect(Theme.of(tester.element(find.text('menuItem'))).brightness, equals(Brightness.light));
+    expect(Theme.of(tester.element(find.text('menuItem')))!.brightness, equals(Brightness.light));
   });
 
   testWidgets('DropdownMenu inherits shadowed app theme', (WidgetTester tester) async {
@@ -131,7 +129,7 @@ void main() {
               actions: <Widget>[
                 DropdownButton<String>(
                   key: dropdownMenuButtonKey,
-                  onChanged: (String newValue) { },
+                  onChanged: (String? newValue) { },
                   value: 'menuItem',
                   items: const <DropdownMenuItem<String>>[
                     DropdownMenuItem<String>(
@@ -151,7 +149,7 @@ void main() {
     await tester.pump(const Duration(seconds: 1));
 
     for (final Element item in tester.elementList(find.text('menuItem')))
-      expect(Theme.of(item).brightness, equals(Brightness.light));
+      expect(Theme.of(item)!.brightness, equals(Brightness.light));
   });
 
   testWidgets('ModalBottomSheet inherits shadowed app theme', (WidgetTester tester) async {
@@ -183,7 +181,7 @@ void main() {
 
     await tester.tap(find.text('SHOW'));
     await tester.pump(const Duration(seconds: 1));
-    expect(Theme.of(tester.element(find.text('bottomSheet'))).brightness, equals(Brightness.light));
+    expect(Theme.of(tester.element(find.text('bottomSheet')))!.brightness, equals(Brightness.light));
 
     await tester.tap(find.text('bottomSheet')); // dismiss the bottom sheet
     await tester.pump(const Duration(seconds: 1));
@@ -220,7 +218,7 @@ void main() {
 
     await tester.tap(find.text('SHOW'));
     await tester.pump(const Duration(seconds: 1));
-    expect(Theme.of(tester.element(find.text('dialog'))).brightness, equals(Brightness.light));
+    expect(Theme.of(tester.element(find.text('dialog')))!.brightness, equals(Brightness.light));
   });
 
   testWidgets("Scaffold inherits theme's scaffoldBackgroundColor", (WidgetTester tester) async {
@@ -275,8 +273,8 @@ void main() {
 
     RenderParagraph glyphText = tester.renderObject(find.byType(RichText));
 
-    expect(glyphText.text.style.color, Colors.green);
-    expect(glyphText.text.style.fontSize, 10.0);
+    expect(glyphText.text.style!.color, Colors.green);
+    expect(glyphText.text.style!.fontSize, 10.0);
 
     await tester.pumpWidget(
       MaterialApp(
@@ -288,14 +286,14 @@ void main() {
 
     glyphText = tester.renderObject(find.byType(RichText));
 
-    expect(glyphText.text.style.color, Color.lerp(Colors.green, Colors.orange, 0.5));
-    expect(glyphText.text.style.fontSize, 15.0);
+    expect(glyphText.text.style!.color, Color.lerp(Colors.green, Colors.orange, 0.5));
+    expect(glyphText.text.style!.fontSize, 15.0);
 
     await tester.pump(const Duration(milliseconds: 100)); // Finish the transition
     glyphText = tester.renderObject(find.byType(RichText));
 
-    expect(glyphText.text.style.color, Colors.orange);
-    expect(glyphText.text.style.fontSize, 20.0);
+    expect(glyphText.text.style!.color, Colors.orange);
+    expect(glyphText.text.style!.fontSize, 20.0);
   });
 
   testWidgets(
@@ -338,21 +336,21 @@ void main() {
     final ThemeData fallback = ThemeData.fallback();
     final ThemeData customTheme = fallback.copyWith(
       primaryTextTheme: fallback.primaryTextTheme.copyWith(
-        bodyText2: fallback.primaryTextTheme.bodyText2.copyWith(
+        bodyText2: fallback.primaryTextTheme.bodyText2!.copyWith(
           fontSize: _kMagicFontSize,
         ),
       ),
     );
-    expect(customTheme.primaryTextTheme.bodyText2.fontSize, _kMagicFontSize);
+    expect(customTheme.primaryTextTheme.bodyText2!.fontSize, _kMagicFontSize);
 
-    double actualFontSize;
+    late double actualFontSize;
     await tester.pumpWidget(Directionality(
       textDirection: TextDirection.ltr,
       child: Theme(
         data: customTheme,
         child: Builder(builder: (BuildContext context) {
-          final ThemeData theme = Theme.of(context);
-          actualFontSize = theme.primaryTextTheme.bodyText2.fontSize;
+          final ThemeData theme = Theme.of(context)!;
+          actualFontSize = theme.primaryTextTheme.bodyText2!.fontSize!;
           return Text(
             'A',
             style: theme.primaryTextTheme.bodyText2,
@@ -365,12 +363,12 @@ void main() {
   });
 
   testWidgets('Default Theme provides all basic TextStyle properties', (WidgetTester tester) async {
-    ThemeData theme;
+    late ThemeData theme;
     await tester.pumpWidget(Directionality(
       textDirection: TextDirection.ltr,
       child: Builder(
         builder: (BuildContext context) {
-          theme = Theme.of(context);
+          theme = Theme.of(context)!;
           return const Text('A');
         },
       ),
@@ -378,17 +376,17 @@ void main() {
 
     List<TextStyle> extractStyles(TextTheme textTheme) {
       return <TextStyle>[
-        textTheme.headline1,
-        textTheme.headline2,
-        textTheme.headline3,
-        textTheme.headline4,
-        textTheme.headline5,
-        textTheme.headline6,
-        textTheme.subtitle1,
-        textTheme.bodyText1,
-        textTheme.bodyText2,
-        textTheme.caption,
-        textTheme.button,
+        textTheme.headline1!,
+        textTheme.headline2!,
+        textTheme.headline3!,
+        textTheme.headline4!,
+        textTheme.headline5!,
+        textTheme.headline6!,
+        textTheme.subtitle1!,
+        textTheme.bodyText1!,
+        textTheme.bodyText2!,
+        textTheme.caption!,
+        textTheme.button!,
       ];
     }
 
@@ -413,14 +411,14 @@ void main() {
       }
     }
 
-    expect(theme.textTheme.headline1.debugLabel, '(englishLike display4 2014).merge(blackMountainView headline1)');
+    expect(theme.textTheme.headline1!.debugLabel, '(englishLike display4 2014).merge(blackMountainView headline1)');
   });
 
   group('Cupertino theme', () {
-    int buildCount;
-    CupertinoThemeData actualTheme;
-    IconThemeData actualIconTheme;
-    BuildContext context;
+    late int buildCount;
+    CupertinoThemeData? actualTheme;
+    IconThemeData? actualIconTheme;
+    BuildContext? context;
 
     final Widget singletonThemeSubtree = Builder(
       builder: (BuildContext localContext) {
@@ -434,7 +432,7 @@ void main() {
 
     Future<CupertinoThemeData> testTheme(WidgetTester tester, ThemeData theme) async {
       await tester.pumpWidget(Theme(data: theme, child: singletonThemeSubtree));
-      return actualTheme;
+      return actualTheme!;
     }
 
     setUp(() {
@@ -468,23 +466,23 @@ void main() {
 
     testWidgets('MaterialTheme overrides the brightness', (WidgetTester tester) async {
       await testTheme(tester, ThemeData.dark());
-      expect(CupertinoTheme.brightnessOf(context), Brightness.dark);
+      expect(CupertinoTheme.brightnessOf(context!), Brightness.dark);
 
       await testTheme(tester, ThemeData.light());
-      expect(CupertinoTheme.brightnessOf(context), Brightness.light);
+      expect(CupertinoTheme.brightnessOf(context!), Brightness.light);
 
       // Overridable by cupertinoOverrideTheme.
       await testTheme(tester, ThemeData(
         brightness: Brightness.light,
         cupertinoOverrideTheme: const CupertinoThemeData(brightness: Brightness.dark),
       ));
-      expect(CupertinoTheme.brightnessOf(context), Brightness.dark);
+      expect(CupertinoTheme.brightnessOf(context!), Brightness.dark);
 
       await testTheme(tester, ThemeData(
         brightness: Brightness.dark,
         cupertinoOverrideTheme: const CupertinoThemeData(brightness: Brightness.light),
       ));
-      expect(CupertinoTheme.brightnessOf(context), Brightness.light);
+      expect(CupertinoTheme.brightnessOf(context!), Brightness.light);
     });
 
     testWidgets('Can override material theme', (WidgetTester tester) async {
@@ -544,7 +542,7 @@ void main() {
         ));
 
         expect(buildCount, 1);
-        expect(actualIconTheme.color, materialIconColor);
+        expect(actualIconTheme!.color, materialIconColor);
     });
 
     testWidgets(
@@ -674,9 +672,9 @@ void main() {
   });
 }
 
-int testBuildCalled;
+int testBuildCalled = 0;
 class Test extends StatefulWidget {
-  const Test({ Key key }) : super(key: key);
+  const Test({ Key? key }) : super(key: key);
 
   @override
   _TestState createState() => _TestState();
@@ -688,7 +686,7 @@ class _TestState extends State<Test> {
     testBuildCalled += 1;
     return Container(
       decoration: BoxDecoration(
-        color: Theme.of(context).primaryColor,
+        color: Theme.of(context)!.primaryColor,
       ),
     );
   }
@@ -704,56 +702,56 @@ class _TextStyleProxy implements TextStyle {
 
   // Do make sure that all the properties correctly forward to the _delegate.
   @override
-  Color get color => _delegate.color;
+  Color? get color => _delegate.color;
   @override
-  Color get backgroundColor => _delegate.backgroundColor;
+  Color? get backgroundColor => _delegate.backgroundColor;
   @override
-  String get debugLabel => _delegate.debugLabel;
+  String? get debugLabel => _delegate.debugLabel;
   @override
-  TextDecoration get decoration => _delegate.decoration;
+  TextDecoration? get decoration => _delegate.decoration;
   @override
-  Color get decorationColor => _delegate.decorationColor;
+  Color? get decorationColor => _delegate.decorationColor;
   @override
-  TextDecorationStyle get decorationStyle => _delegate.decorationStyle;
+  TextDecorationStyle? get decorationStyle => _delegate.decorationStyle;
   @override
-  double get decorationThickness => _delegate.decorationThickness;
+  double? get decorationThickness => _delegate.decorationThickness;
   @override
-  String get fontFamily => _delegate.fontFamily;
+  String? get fontFamily => _delegate.fontFamily;
   @override
-  List<String> get fontFamilyFallback => _delegate.fontFamilyFallback;
+  List<String>? get fontFamilyFallback => _delegate.fontFamilyFallback;
   @override
-  double get fontSize => _delegate.fontSize;
+  double? get fontSize => _delegate.fontSize;
   @override
-  FontStyle get fontStyle => _delegate.fontStyle;
+  FontStyle? get fontStyle => _delegate.fontStyle;
   @override
-  FontWeight get fontWeight => _delegate.fontWeight;
+  FontWeight? get fontWeight => _delegate.fontWeight;
   @override
-  double get height => _delegate.height;
+  double? get height => _delegate.height;
   @override
-  Locale get locale => _delegate.locale;
+  Locale? get locale => _delegate.locale;
   @override
-  ui.Paint get foreground => _delegate.foreground;
+  ui.Paint? get foreground => _delegate.foreground;
   @override
-  ui.Paint get background => _delegate.background;
+  ui.Paint? get background => _delegate.background;
   @override
   bool get inherit => _delegate.inherit;
   @override
-  double get letterSpacing => _delegate.letterSpacing;
+  double? get letterSpacing => _delegate.letterSpacing;
   @override
-  TextBaseline get textBaseline => _delegate.textBaseline;
+  TextBaseline? get textBaseline => _delegate.textBaseline;
   @override
-  double get wordSpacing => _delegate.wordSpacing;
+  double? get wordSpacing => _delegate.wordSpacing;
   @override
-  List<Shadow> get shadows => _delegate.shadows;
+  List<Shadow>? get shadows => _delegate.shadows;
   @override
-  List<ui.FontFeature> get fontFeatures => _delegate.fontFeatures;
+  List<ui.FontFeature>? get fontFeatures => _delegate.fontFeatures;
 
   @override
   String toString({ DiagnosticLevel minLevel = DiagnosticLevel.info }) =>
       super.toString();
 
   @override
-  DiagnosticsNode toDiagnosticsNode({ String name, DiagnosticsTreeStyle style }) {
+  DiagnosticsNode toDiagnosticsNode({ String? name, DiagnosticsTreeStyle? style }) {
     throw UnimplementedError();
   }
 
@@ -764,29 +762,29 @@ class _TextStyleProxy implements TextStyle {
 
   @override
   TextStyle apply({
-    Color color,
-    Color backgroundColor,
-    TextDecoration decoration,
-    Color decorationColor,
-    TextDecorationStyle decorationStyle,
+    Color? color,
+    Color? backgroundColor,
+    TextDecoration? decoration,
+    Color? decorationColor,
+    TextDecorationStyle? decorationStyle,
     double decorationThicknessFactor = 1.0,
     double decorationThicknessDelta = 0.0,
-    String fontFamily,
-    List<String> fontFamilyFallback,
+    String? fontFamily,
+    List<String>? fontFamilyFallback,
     double fontSizeFactor = 1.0,
     double fontSizeDelta = 0.0,
     int fontWeightDelta = 0,
-    FontStyle fontStyle,
+    FontStyle? fontStyle,
     double letterSpacingFactor = 1.0,
     double letterSpacingDelta = 0.0,
     double wordSpacingFactor = 1.0,
     double wordSpacingDelta = 0.0,
     double heightFactor = 1.0,
     double heightDelta = 0.0,
-    TextBaseline textBaseline,
-    Locale locale,
-    List<ui.Shadow> shadows,
-    List<ui.FontFeature> fontFeatures,
+    TextBaseline? textBaseline,
+    Locale? locale,
+    List<ui.Shadow>? shadows,
+    List<ui.FontFeature>? fontFeatures,
   }) {
     throw UnimplementedError();
   }
@@ -798,28 +796,28 @@ class _TextStyleProxy implements TextStyle {
 
   @override
   TextStyle copyWith({
-    bool inherit,
-    Color color,
-    Color backgroundColor,
-    String fontFamily,
-    List<String> fontFamilyFallback,
-    double fontSize,
-    FontWeight fontWeight,
-    FontStyle fontStyle,
-    double letterSpacing,
-    double wordSpacing,
-    TextBaseline textBaseline,
-    double height,
-    Locale locale,
-    ui.Paint foreground,
-    ui.Paint background,
-    List<Shadow> shadows,
-    List<ui.FontFeature> fontFeatures,
-    TextDecoration decoration,
-    Color decorationColor,
-    TextDecorationStyle decorationStyle,
-    double decorationThickness,
-    String debugLabel,
+    bool? inherit,
+    Color? color,
+    Color? backgroundColor,
+    String? fontFamily,
+    List<String>? fontFamilyFallback,
+    double? fontSize,
+    FontWeight? fontWeight,
+    FontStyle? fontStyle,
+    double? letterSpacing,
+    double? wordSpacing,
+    TextBaseline? textBaseline,
+    double? height,
+    Locale? locale,
+    ui.Paint? foreground,
+    ui.Paint? background,
+    List<Shadow>? shadows,
+    List<ui.FontFeature>? fontFeatures,
+    TextDecoration? decoration,
+    Color? decorationColor,
+    TextDecorationStyle? decorationStyle,
+    double? decorationThickness,
+    String? debugLabel,
   }) {
     throw UnimplementedError();
   }
@@ -831,19 +829,19 @@ class _TextStyleProxy implements TextStyle {
 
   @override
   ui.ParagraphStyle getParagraphStyle({
-    TextAlign textAlign,
-    TextDirection textDirection,
+    TextAlign? textAlign,
+    TextDirection? textDirection,
     double textScaleFactor = 1.0,
-    String ellipsis,
-    int maxLines,
-    ui.TextHeightBehavior textHeightBehavior,
-    Locale locale,
-    String fontFamily,
-    double fontSize,
-    FontWeight fontWeight,
-    FontStyle fontStyle,
-    double height,
-    StrutStyle strutStyle,
+    String? ellipsis,
+    int? maxLines,
+    ui.TextHeightBehavior? textHeightBehavior,
+    Locale? locale,
+    String? fontFamily,
+    double? fontSize,
+    FontWeight? fontWeight,
+    FontStyle? fontStyle,
+    double? height,
+    StrutStyle? strutStyle,
   }) {
     throw UnimplementedError();
   }
@@ -854,7 +852,7 @@ class _TextStyleProxy implements TextStyle {
   }
 
   @override
-  TextStyle merge(TextStyle other) {
+  TextStyle merge(TextStyle? other) {
     throw UnimplementedError();
   }
 }

packages/flutter/test/material/time_picker_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 @TestOn('!chrome') // entire file needs triage.
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -19,14 +17,14 @@ final Finder _timePickerDialog = find.byWidgetPredicate((Widget widget) => '${wi
 
 class _TimePickerLauncher extends StatelessWidget {
   const _TimePickerLauncher({
-    Key key,
-    this.onChanged,
+    Key? key,
+    required this.onChanged,
     this.locale,
     this.entryMode = TimePickerEntryMode.dial,
   }) : super(key: key);
 
   final ValueChanged<TimeOfDay> onChanged;
-  final Locale locale;
+  final Locale? locale;
   final TimePickerEntryMode entryMode;
 
   @override
@@ -55,7 +53,7 @@ class _TimePickerLauncher extends StatelessWidget {
   }
 }
 
-Future<Offset> startPicker(
+Future<Offset?> startPicker(
     WidgetTester tester,
     ValueChanged<TimeOfDay> onChanged, {
       TimePickerEntryMode entryMode = TimePickerEntryMode.dial,
@@ -67,7 +65,7 @@ Future<Offset> startPicker(
 }
 
 Future<void> finishPicker(WidgetTester tester) async {
-  final MaterialLocalizations materialLocalizations = MaterialLocalizations.of(tester.element(find.byType(ElevatedButton)));
+  final MaterialLocalizations materialLocalizations = MaterialLocalizations.of(tester.element(find.byType(ElevatedButton)))!;
   await tester.tap(find.text(materialLocalizations.okButtonLabel));
   await tester.pumpAndSettle(const Duration(seconds: 1));
 }
@@ -84,24 +82,24 @@ void main() {
 
 void _tests() {
   testWidgets('tap-select an hour', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
 
-    Offset center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    Offset center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     await tester.tapAt(Offset(center.dx, center.dy - 50.0)); // 12:00 AM
     await finishPicker(tester);
     expect(result, equals(const TimeOfDay(hour: 0, minute: 0)));
 
-    center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     await tester.tapAt(Offset(center.dx + 50.0, center.dy));
     await finishPicker(tester);
     expect(result, equals(const TimeOfDay(hour: 3, minute: 0)));
 
-    center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     await tester.tapAt(Offset(center.dx, center.dy + 50.0));
     await finishPicker(tester);
     expect(result, equals(const TimeOfDay(hour: 6, minute: 0)));
 
-    center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     await tester.tapAt(Offset(center.dx, center.dy + 50.0));
     await tester.tapAt(Offset(center.dx - 50, center.dy));
     await finishPicker(tester);
@@ -109,9 +107,9 @@ void _tests() {
   });
 
   testWidgets('drag-select an hour', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
 
-    final Offset center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    final Offset center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     final Offset hour0 = Offset(center.dx, center.dy - 50.0); // 12:00 AM
     final Offset hour3 = Offset(center.dx + 50.0, center.dy);
     final Offset hour6 = Offset(center.dx, center.dy + 50.0);
@@ -148,9 +146,9 @@ void _tests() {
   });
 
   testWidgets('tap-select switches from hour to minute', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
 
-    final Offset center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    final Offset center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     final Offset hour6 = Offset(center.dx, center.dy + 50.0); // 6:00
     final Offset min45 = Offset(center.dx - 50.0, center.dy); // 45 mins (or 9:00 hours)
 
@@ -162,9 +160,9 @@ void _tests() {
   });
 
   testWidgets('drag-select switches from hour to minute', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
 
-    final Offset center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    final Offset center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     final Offset hour3 = Offset(center.dx + 50.0, center.dy);
     final Offset hour6 = Offset(center.dx, center.dy + 50.0);
     final Offset hour9 = Offset(center.dx - 50.0, center.dy);
@@ -181,9 +179,9 @@ void _tests() {
   });
 
   testWidgets('tap-select rounds down to nearest 5 minute increment', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
 
-    final Offset center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    final Offset center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     final Offset hour6 = Offset(center.dx, center.dy + 50.0); // 6:00
     final Offset min46 = Offset(center.dx - 50.0, center.dy - 5); // 46 mins
 
@@ -195,9 +193,9 @@ void _tests() {
   });
 
   testWidgets('tap-select rounds up to nearest 5 minute increment', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
 
-    final Offset center = await startPicker(tester, (TimeOfDay time) { result = time; });
+    final Offset center = (await startPicker(tester, (TimeOfDay time) { result = time; }))!;
     final Offset hour6 = Offset(center.dx, center.dy + 50.0); // 6:00
     final Offset min48 = Offset(center.dx - 50.0, center.dy - 15); // 48 mins
 
@@ -211,25 +209,25 @@ void _tests() {
   group('haptic feedback', () {
     const Duration kFastFeedbackInterval = Duration(milliseconds: 10);
     const Duration kSlowFeedbackInterval = Duration(milliseconds: 200);
-    FeedbackTester feedback;
+    late FeedbackTester feedback;
 
     setUp(() {
       feedback = FeedbackTester();
     });
 
     tearDown(() {
-      feedback?.dispose();
+      feedback.dispose();
     });
 
     testWidgets('tap-select vibrates once', (WidgetTester tester) async {
-      final Offset center = await startPicker(tester, (TimeOfDay time) { });
+      final Offset center = (await startPicker(tester, (TimeOfDay time) { }))!;
       await tester.tapAt(Offset(center.dx, center.dy - 50.0));
       await finishPicker(tester);
       expect(feedback.hapticCount, 1);
     });
 
     testWidgets('quick successive tap-selects vibrate once', (WidgetTester tester) async {
-      final Offset center = await startPicker(tester, (TimeOfDay time) { });
+      final Offset center = (await startPicker(tester, (TimeOfDay time) { }))!;
       await tester.tapAt(Offset(center.dx, center.dy - 50.0));
       await tester.pump(kFastFeedbackInterval);
       await tester.tapAt(Offset(center.dx, center.dy + 50.0));
@@ -238,7 +236,7 @@ void _tests() {
     });
 
     testWidgets('slow successive tap-selects vibrate once per tap', (WidgetTester tester) async {
-      final Offset center = await startPicker(tester, (TimeOfDay time) { });
+      final Offset center = (await startPicker(tester, (TimeOfDay time) { }))!;
       await tester.tapAt(Offset(center.dx, center.dy - 50.0));
       await tester.pump(kSlowFeedbackInterval);
       await tester.tapAt(Offset(center.dx, center.dy + 50.0));
@@ -249,7 +247,7 @@ void _tests() {
     });
 
     testWidgets('drag-select vibrates once', (WidgetTester tester) async {
-      final Offset center = await startPicker(tester, (TimeOfDay time) { });
+      final Offset center = (await startPicker(tester, (TimeOfDay time) { }))!;
       final Offset hour0 = Offset(center.dx, center.dy - 50.0);
       final Offset hour3 = Offset(center.dx + 50.0, center.dy);
 
@@ -261,7 +259,7 @@ void _tests() {
     });
 
     testWidgets('quick drag-select vibrates once', (WidgetTester tester) async {
-      final Offset center = await startPicker(tester, (TimeOfDay time) { });
+      final Offset center = (await startPicker(tester, (TimeOfDay time) { }))!;
       final Offset hour0 = Offset(center.dx, center.dy - 50.0);
       final Offset hour3 = Offset(center.dx + 50.0, center.dy);
 
@@ -277,7 +275,7 @@ void _tests() {
     });
 
     testWidgets('slow drag-select vibrates once', (WidgetTester tester) async {
-      final Offset center = await startPicker(tester, (TimeOfDay time) { });
+      final Offset center = (await startPicker(tester, (TimeOfDay time) { }))!;
       final Offset hour0 = Offset(center.dx, center.dy - 50.0);
       final Offset hour3 = Offset(center.dx + 50.0, center.dy);
 
@@ -403,12 +401,12 @@ void _tests() {
   testWidgets('can increment and decrement hours', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);
 
-    Future<void> actAndExpect({ String initialValue, SemanticsAction action, String finalValue }) async {
+    Future<void> actAndExpect({ required String initialValue, required SemanticsAction action, required String finalValue }) async {
       final SemanticsNode elevenHours = semantics.nodesWith(
         value: 'Select hours $initialValue',
         ancestor: tester.renderObject(_hourControl).debugSemantics,
       ).single;
-      tester.binding.pipelineOwner.semanticsOwner.performAction(elevenHours.id, action);
+      tester.binding.pipelineOwner.semanticsOwner!.performAction(elevenHours.id, action);
       await tester.pumpAndSettle();
       expect(
         find.descendant(of: _hourControl, matching: find.text(finalValue)),
@@ -430,7 +428,7 @@ void _tests() {
     );
 
     // Ensure we preserve day period as we roll over.
-    final dynamic pickerState = tester.state(_timePickerDialog);
+    final dynamic pickerState = tester.state(_timePickerDialog); // ignore: unnecessary_nullable_for_final_variable_declarations
     expect(pickerState.selectedTime, const TimeOfDay(hour: 1, minute: 0));
 
     await actAndExpect(
@@ -469,12 +467,12 @@ void _tests() {
   testWidgets('can increment and decrement minutes', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);
 
-    Future<void> actAndExpect({ String initialValue, SemanticsAction action, String finalValue }) async {
+    Future<void> actAndExpect({ required String initialValue, required SemanticsAction action, required String finalValue }) async {
       final SemanticsNode elevenHours = semantics.nodesWith(
         value: 'Select minutes $initialValue',
         ancestor: tester.renderObject(_minuteControl).debugSemantics,
       ).single;
-      tester.binding.pipelineOwner.semanticsOwner.performAction(elevenHours.id, action);
+      tester.binding.pipelineOwner.semanticsOwner!.performAction(elevenHours.id, action);
       await tester.pumpAndSettle();
       expect(
         find.descendant(of: _minuteControl, matching: find.text(finalValue)),
@@ -495,7 +493,7 @@ void _tests() {
     );
 
     // Ensure we preserve hour period as we roll over.
-    final dynamic pickerState = tester.state(_timePickerDialog);
+    final dynamic pickerState = tester.state(_timePickerDialog); // ignore: unnecessary_nullable_for_final_variable_declarations
     expect(pickerState.selectedTime, const TimeOfDay(hour: 11, minute: 0));
 
     await actAndExpect(
@@ -554,10 +552,10 @@ void _tests() {
                     showTimePicker(
                       context: context,
                       initialTime: const TimeOfDay(hour: 7, minute: 0),
-                      builder: (BuildContext context, Widget child) {
+                      builder: (BuildContext context, Widget? child) {
                         return Directionality(
                           textDirection: textDirection,
-                          child: child,
+                          child: child!,
                         );
                       },
                     );
@@ -705,10 +703,10 @@ void _tests() {
                     showTimePicker(
                       context: context,
                       initialTime: const TimeOfDay(hour: 7, minute: 0),
-                      builder: (BuildContext context, Widget child) {
+                      builder: (BuildContext context, Widget? child) {
                         return Directionality(
                           textDirection: textDirection,
-                          child: child,
+                          child: child!,
                         );
                       },
                     );
@@ -795,7 +793,7 @@ void _testsInput() {
   });
 
   testWidgets('Initial time is the default', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
     await startPicker(tester, (TimeOfDay time) { result = time; }, entryMode: TimePickerEntryMode.input);
     await finishPicker(tester);
     expect(result, equals(const TimeOfDay(hour: 7, minute: 0)));
@@ -899,7 +897,7 @@ void _testsInput() {
   });
 
   testWidgets('Entered text returns time', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
     await startPicker(tester, (TimeOfDay time) { result = time; }, entryMode: TimePickerEntryMode.input);
     await tester.enterText(find.byType(TextField).first, '9');
     await tester.enterText(find.byType(TextField).last, '12');
@@ -908,7 +906,7 @@ void _testsInput() {
   });
 
   testWidgets('Toggle to dial mode keeps selected time', (WidgetTester tester) async {
-    TimeOfDay result;
+    late TimeOfDay result;
     await startPicker(tester, (TimeOfDay time) { result = time; }, entryMode: TimePickerEntryMode.input);
     await tester.enterText(find.byType(TextField).first, '8');
     await tester.enterText(find.byType(TextField).last, '15');
@@ -918,7 +916,7 @@ void _testsInput() {
   });
 
   testWidgets('Invalid text prevents dismissing', (WidgetTester tester) async {
-    TimeOfDay result;
+    TimeOfDay? result;
     await startPicker(tester, (TimeOfDay time) { result = time; }, entryMode: TimePickerEntryMode.input);
 
     // Invalid hour.
@@ -959,7 +957,7 @@ class PickerObserver extends NavigatorObserver {
   int pickerCount = 0;
 
   @override
-  void didPush(Route<dynamic> route, Route<dynamic> previousRoute) {
+  void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
     if (route.toString().contains('_DialogRoute')) {
       pickerCount++;
     }
@@ -973,7 +971,7 @@ Future<void> mediaQueryBoilerplate(
       TimeOfDay initialTime = const TimeOfDay(hour: 7, minute: 0),
       double textScaleFactor = 1.0,
       TimePickerEntryMode entryMode = TimePickerEntryMode.dial,
-      String helpText,
+      String? helpText,
       bool accessibleNavigation = false,
     }) async {
   await tester.pumpWidget(

packages/flutter/test/material/time_picker_theme_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter/painting.dart';
 import 'package:flutter/rendering.dart';
@@ -117,7 +115,7 @@ void main() {
     final RenderParagraph hourText = _textRenderParagraph(tester, '7');
     expect(
       hourText.text.style,
-      Typography.material2014().englishLike.headline2
+      Typography.material2014().englishLike.headline2!
           .merge(Typography.material2014().black.headline2)
           .copyWith(color: defaultTheme.colorScheme.primary),
     );
@@ -125,7 +123,7 @@ void main() {
     final RenderParagraph minuteText = _textRenderParagraph(tester, '15');
     expect(
       minuteText.text.style,
-      Typography.material2014().englishLike.headline2
+      Typography.material2014().englishLike.headline2!
           .merge(Typography.material2014().black.headline2)
           .copyWith(color: defaultTheme.colorScheme.onSurface),
     );
@@ -133,7 +131,7 @@ void main() {
     final RenderParagraph amText = _textRenderParagraph(tester, 'AM');
     expect(
       amText.text.style,
-      Typography.material2014().englishLike.subtitle1
+      Typography.material2014().englishLike.subtitle1!
           .merge(Typography.material2014().black.subtitle1)
           .copyWith(color: defaultTheme.colorScheme.primary),
     );
@@ -141,7 +139,7 @@ void main() {
     final RenderParagraph pmText = _textRenderParagraph(tester, 'PM');
     expect(
       pmText.text.style,
-      Typography.material2014().englishLike.subtitle1
+      Typography.material2014().englishLike.subtitle1!
           .merge(Typography.material2014().black.subtitle1)
           .copyWith(color: defaultTheme.colorScheme.onSurface.withOpacity(0.6)),
     );
@@ -149,7 +147,7 @@ void main() {
     final RenderParagraph helperText = _textRenderParagraph(tester, 'SELECT TIME');
     expect(
       helperText.text.style,
-      Typography.material2014().englishLike.overline
+      Typography.material2014().englishLike.overline!
           .merge(Typography.material2014().black.overline),
     );
 
@@ -158,14 +156,14 @@ void main() {
     final List<dynamic> primaryLabels = dialPainter.primaryLabels as List<dynamic>;
     expect(
       primaryLabels.first.painter.text.style,
-      Typography.material2014().englishLike.bodyText1
+      Typography.material2014().englishLike.bodyText1!
         .merge(Typography.material2014().black.bodyText1)
         .copyWith(color: defaultTheme.colorScheme.onSurface),
     );
     final List<dynamic> secondaryLabels = dialPainter.secondaryLabels as List<dynamic>;
     expect(
       secondaryLabels.first.painter.text.style,
-      Typography.material2014().englishLike.bodyText1
+      Typography.material2014().englishLike.bodyText1!
         .merge(Typography.material2014().white.bodyText1)
         .copyWith(color: defaultTheme.colorScheme.onPrimary),
     );
@@ -217,7 +215,7 @@ void main() {
     await tester.tap(find.text('X'));
     await tester.pumpAndSettle(const Duration(seconds: 1));
 
-    final InputDecoration hourDecoration = _textField(tester, '7').decoration;
+    final InputDecoration hourDecoration = _textField(tester, '7').decoration!;
     expect(hourDecoration.filled, true);
     expect(hourDecoration.fillColor, defaultTheme.colorScheme.onSurface.withOpacity(0.12));
     expect(hourDecoration.enabledBorder, const OutlineInputBorder(borderSide: BorderSide(color: Colors.transparent)));
@@ -226,8 +224,8 @@ void main() {
     expect(hourDecoration.focusedErrorBorder, OutlineInputBorder(borderSide: BorderSide(color: defaultTheme.colorScheme.error, width: 2)));
     expect(
       hourDecoration.hintStyle,
-      Typography.material2014().englishLike.headline2
-          .merge(defaultTheme.textTheme.headline2.copyWith(color: defaultTheme.colorScheme.onSurface.withOpacity(0.36))),
+      Typography.material2014().englishLike.headline2!
+          .merge(defaultTheme.textTheme.headline2!.copyWith(color: defaultTheme.colorScheme.onSurface.withOpacity(0.36))),
     );
   });
 
@@ -246,14 +244,14 @@ void main() {
     expect(
       dial,
       paints
-        ..circle(color: Color(timePickerTheme.dialBackgroundColor.value)) // Dial background color.
-        ..circle(color: Color(timePickerTheme.dialHandColor.value)), // Dial hand color.
+        ..circle(color: Color(timePickerTheme.dialBackgroundColor!.value)) // Dial background color.
+        ..circle(color: Color(timePickerTheme.dialHandColor!.value)), // Dial hand color.
     );
 
     final RenderParagraph hourText = _textRenderParagraph(tester, '7');
     expect(
       hourText.text.style,
-      Typography.material2014().englishLike.bodyText2
+      Typography.material2014().englishLike.bodyText2!
           .merge(Typography.material2014().black.bodyText2)
           .merge(timePickerTheme.hourMinuteTextStyle)
           .copyWith(color: _selectedColor),
@@ -262,7 +260,7 @@ void main() {
     final RenderParagraph minuteText = _textRenderParagraph(tester, '15');
     expect(
       minuteText.text.style,
-      Typography.material2014().englishLike.bodyText2
+      Typography.material2014().englishLike.bodyText2!
           .merge(Typography.material2014().black.bodyText2)
           .merge(timePickerTheme.hourMinuteTextStyle)
           .copyWith(color: _unselectedColor),
@@ -271,7 +269,7 @@ void main() {
     final RenderParagraph amText = _textRenderParagraph(tester, 'AM');
     expect(
       amText.text.style,
-      Typography.material2014().englishLike.subtitle1
+      Typography.material2014().englishLike.subtitle1!
           .merge(Typography.material2014().black.subtitle1)
           .merge(timePickerTheme.dayPeriodTextStyle)
           .copyWith(color: _selectedColor),
@@ -280,7 +278,7 @@ void main() {
     final RenderParagraph pmText = _textRenderParagraph(tester, 'PM');
     expect(
       pmText.text.style,
-      Typography.material2014().englishLike.subtitle1
+      Typography.material2014().englishLike.subtitle1!
           .merge(Typography.material2014().black.subtitle1)
           .merge(timePickerTheme.dayPeriodTextStyle)
           .copyWith(color: _unselectedColor),
@@ -289,7 +287,7 @@ void main() {
     final RenderParagraph helperText = _textRenderParagraph(tester, 'SELECT TIME');
     expect(
       helperText.text.style,
-      Typography.material2014().englishLike.bodyText2
+      Typography.material2014().englishLike.bodyText2!
           .merge(Typography.material2014().black.bodyText2)
           .merge(timePickerTheme.helpTextStyle),
     );
@@ -299,14 +297,14 @@ void main() {
     final List<dynamic> primaryLabels = dialPainter.primaryLabels as List<dynamic>;
     expect(
       primaryLabels.first.painter.text.style,
-      Typography.material2014().englishLike.bodyText1
+      Typography.material2014().englishLike.bodyText1!
           .merge(Typography.material2014().black.bodyText1)
           .copyWith(color: _unselectedColor),
     );
     final List<dynamic> secondaryLabels = dialPainter.secondaryLabels as List<dynamic>;
     expect(
       secondaryLabels.first.painter.text.style,
-      Typography.material2014().englishLike.bodyText1
+      Typography.material2014().englishLike.bodyText1!
           .merge(Typography.material2014().white.bodyText1)
           .copyWith(color: _selectedColor),
     );
@@ -328,13 +326,13 @@ void main() {
     final Material dayPeriodMaterial = _dayPeriodMaterial(tester);
     expect(
       dayPeriodMaterial.shape,
-      timePickerTheme.dayPeriodShape.copyWith(side: timePickerTheme.dayPeriodBorderSide),
+      timePickerTheme.dayPeriodShape!.copyWith(side: timePickerTheme.dayPeriodBorderSide),
     );
 
     final Container dayPeriodDivider = _dayPeriodDivider(tester);
     expect(
       dayPeriodDivider.decoration,
-      BoxDecoration(border: Border(left: timePickerTheme.dayPeriodBorderSide)),
+      BoxDecoration(border: Border(left: timePickerTheme.dayPeriodBorderSide!)),
     );
 
     final IconButton entryModeIconButton = _entryModeIconButton(tester);
@@ -351,14 +349,14 @@ void main() {
     await tester.tap(find.text('X'));
     await tester.pumpAndSettle(const Duration(seconds: 1));
 
-    final InputDecoration hourDecoration = _textField(tester, '7').decoration;
-    expect(hourDecoration.filled, timePickerTheme.inputDecorationTheme.filled);
-    expect(hourDecoration.fillColor, timePickerTheme.inputDecorationTheme.fillColor);
-    expect(hourDecoration.enabledBorder, timePickerTheme.inputDecorationTheme.enabledBorder);
-    expect(hourDecoration.errorBorder, timePickerTheme.inputDecorationTheme.errorBorder);
-    expect(hourDecoration.focusedBorder, timePickerTheme.inputDecorationTheme.focusedBorder);
-    expect(hourDecoration.focusedErrorBorder, timePickerTheme.inputDecorationTheme.focusedErrorBorder);
-    expect(hourDecoration.hintStyle, timePickerTheme.inputDecorationTheme.hintStyle);
+    final InputDecoration hourDecoration = _textField(tester, '7').decoration!;
+    expect(hourDecoration.filled, timePickerTheme.inputDecorationTheme!.filled);
+    expect(hourDecoration.fillColor, timePickerTheme.inputDecorationTheme!.fillColor);
+    expect(hourDecoration.enabledBorder, timePickerTheme.inputDecorationTheme!.enabledBorder);
+    expect(hourDecoration.errorBorder, timePickerTheme.inputDecorationTheme!.errorBorder);
+    expect(hourDecoration.focusedBorder, timePickerTheme.inputDecorationTheme!.focusedBorder);
+    expect(hourDecoration.focusedErrorBorder, timePickerTheme.inputDecorationTheme!.focusedErrorBorder);
+    expect(hourDecoration.hintStyle, timePickerTheme.inputDecorationTheme!.hintStyle);
   });
 
   testWidgets('Time picker uses values from TimePickerThemeData without InputDecorationTheme - input mode', (WidgetTester tester) async {
@@ -368,13 +366,13 @@ void main() {
     await tester.tap(find.text('X'));
     await tester.pumpAndSettle(const Duration(seconds: 1));
 
-    final InputDecoration hourDecoration = _textField(tester, '7').decoration;
+    final InputDecoration hourDecoration = _textField(tester, '7').decoration!;
     expect(hourDecoration.fillColor, timePickerTheme.hourMinuteColor);
   });
 }
 
-final Color _selectedColor = Colors.green[100];
-final Color _unselectedColor = Colors.green[200];
+final Color _selectedColor = Colors.green[100]!;
+final Color _unselectedColor = Colors.green[200]!;
 
 TimePickerThemeData _timePickerTheme({bool includeInputDecoration = false}) {
   Color getColor(Set<MaterialState> states) {
@@ -412,12 +410,12 @@ TimePickerThemeData _timePickerTheme({bool includeInputDecoration = false}) {
 
 class _TimePickerLauncher extends StatelessWidget {
   const _TimePickerLauncher({
-    Key key,
+    Key? key,
     this.themeData,
     this.entryMode = TimePickerEntryMode.dial,
   }) : super(key: key);
 
-  final ThemeData themeData;
+  final ThemeData? themeData;
   final TimePickerEntryMode entryMode;
 
   @override
@@ -471,7 +469,7 @@ IconButton _entryModeIconButton(WidgetTester tester) {
 }
 
 RenderParagraph _textRenderParagraph(WidgetTester tester, String text) {
-  return tester.element<StatelessElement>(find.text(text).first).renderObject as RenderParagraph;
+  return tester.element<StatelessElement>(find.text(text).first).renderObject! as RenderParagraph;
 }
 
 final Finder findDialPaint = find.descendant(

packages/flutter/test/material/time_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -11,7 +9,7 @@ void main() {
   group('TimeOfDay.format', () {
     testWidgets('respects alwaysUse24HourFormat option', (WidgetTester tester) async {
       Future<String> pumpTest(bool alwaysUse24HourFormat) async {
-        String formattedValue;
+        late String formattedValue;
         await tester.pumpWidget(MaterialApp(
           home: MediaQuery(
             data: MediaQueryData(alwaysUse24HourFormat: alwaysUse24HourFormat),

packages/flutter/test/material/toggle_buttons_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -13,7 +11,7 @@ import '../rendering/mock_canvas.dart';
 
 const double _defaultBorderWidth = 1.0;
 
-Widget boilerplate({Widget child}) {
+Widget boilerplate({required Widget child}) {
   return Directionality(
     textDirection: TextDirection.ltr,
     child: Center(child: child),
@@ -170,50 +168,6 @@ void main() {
     },
   );
 
-  testWidgets('children property cannot be null', (WidgetTester tester) async {
-    try {
-      await tester.pumpWidget(
-        Material(
-          child: boilerplate(
-            child: ToggleButtons(
-              isSelected: const <bool>[false, true],
-              onPressed: (int index) {},
-              children: null,
-            ),
-          ),
-        ),
-      );
-      fail('Should not be possible to create a toggle button with no children.');
-    } on AssertionError catch (e) {
-      expect(e.toString(), contains('children != null'));
-    }
-  });
-
-  testWidgets(
-    'isSelected property cannot be null',
-    (WidgetTester tester) async {
-      try {
-        await tester.pumpWidget(
-          Material(
-            child: boilerplate(
-              child: ToggleButtons(
-                isSelected: null,
-                onPressed: (int index) {},
-                children: const <Widget>[
-                  Text('First child'),
-                  Text('Second child'),
-                ],
-              ),
-            ),
-          ),
-        );
-        fail('Should not be possible to create a toggle button with no isSelected.');
-      } on AssertionError catch (e) {
-        expect(e.toString(), contains('isSelected != null'));
-      }
-    },
-  );
-
   testWidgets(
     'children and isSelected properties have to be the same length',
     (WidgetTester tester) async {
@@ -262,15 +216,15 @@ void main() {
         of: find.widgetWithText(RawMaterialButton, 'First child'),
         matching: find.byType(DefaultTextStyle),
     )).style;
-    expect(textStyle.fontFamily, theme.textTheme.bodyText2.fontFamily);
-    expect(textStyle.decoration, theme.textTheme.bodyText2.decoration);
+    expect(textStyle.fontFamily, theme.textTheme.bodyText2!.fontFamily);
+    expect(textStyle.decoration, theme.textTheme.bodyText2!.decoration);
 
     textStyle = tester.widget<DefaultTextStyle>(find.descendant(
         of: find.widgetWithText(RawMaterialButton, 'Second child'),
         matching: find.byType(DefaultTextStyle),
     )).style;
-    expect(textStyle.fontFamily, theme.textTheme.bodyText2.fontFamily);
-    expect(textStyle.decoration, theme.textTheme.bodyText2.decoration);
+    expect(textStyle.fontFamily, theme.textTheme.bodyText2!.fontFamily);
+    expect(textStyle.decoration, theme.textTheme.bodyText2!.decoration);
   });
 
   testWidgets('Custom text style except color is applied', (WidgetTester tester) async {
@@ -1470,7 +1424,7 @@ void main() {
 
     await tester.pump();
 
-    expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.text);
+    expect(RendererBinding.instance!.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.text);
 
     // Test default cursor
     await tester.pumpWidget(
@@ -1491,7 +1445,7 @@ void main() {
       ),
     );
 
-    expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.click);
+    expect(RendererBinding.instance!.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.click);
 
     // Test default cursor when disabled
     await tester.pumpWidget(
@@ -1511,6 +1465,6 @@ void main() {
       ),
     );
 
-    expect(RendererBinding.instance.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.basic);
+    expect(RendererBinding.instance!.mouseTracker.debugDeviceActiveCursor(1), SystemMouseCursors.basic);
   });
 }

packages/flutter/test/material/toggle_buttons_theme_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -11,7 +9,7 @@ import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';
 
-Widget boilerplate({Widget child}) {
+Widget boilerplate({required Widget child}) {
   return Directionality(
     textDirection: TextDirection.ltr,
     child: Center(child: child),

packages/flutter/test/material/tooltip_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:ui';
 
 import 'package:flutter/services.dart';
@@ -581,7 +579,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style;
+    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style!;
     expect(textStyle.color, Colors.white);
     expect(textStyle.fontFamily, 'Roboto');
     expect(textStyle.decoration, TextDecoration.none);
@@ -607,7 +605,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style;
+    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style!;
     expect(textStyle.color, Colors.black);
     expect(textStyle.fontFamily, 'Roboto');
     expect(textStyle.decoration, TextDecoration.none);
@@ -634,7 +632,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style;
+    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style!;
     expect(textStyle.color, Colors.orange);
     expect(textStyle.fontFamily, null);
     expect(textStyle.decoration, TextDecoration.underline);
@@ -833,12 +831,12 @@ void main() {
 
   testWidgets('Tooltip shows/hides when hovered', (WidgetTester tester) async {
     const Duration waitDuration = Duration(milliseconds: 0);
-    TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+    TestGesture? gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     addTearDown(() async {
       if (gesture != null)
         return gesture.removePointer();
     });
-    await gesture.addPointer();
+    await gesture!.addPointer();
     await gesture.moveTo(const Offset(1.0, 1.0));
     await tester.pump();
     await gesture.moveTo(Offset.zero);
@@ -1013,7 +1011,7 @@ void main() {
   });
 
   testWidgets('Tooltip text scales with textScaleFactor', (WidgetTester tester) async {
-    Widget buildApp(String text, { double textScaleFactor }) {
+    Widget buildApp(String text, { required double textScaleFactor }) {
       return MediaQuery(
         data: MediaQueryData(textScaleFactor: textScaleFactor),
         child: Directionality(
@@ -1254,6 +1252,6 @@ void main() {
 
 SemanticsNode findDebugSemantics(RenderObject object) {
   if (object.debugSemantics != null)
-    return object.debugSemantics;
-  return findDebugSemantics(object.parent as RenderObject);
+    return object.debugSemantics!;
+  return findDebugSemantics(object.parent! as RenderObject);
 }

packages/flutter/test/material/tooltip_theme_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/services.dart';
 import 'package:flutter/src/material/tooltip_theme.dart';
 import 'package:flutter/gestures.dart';
@@ -151,7 +149,7 @@ void main() {
      *                   *
      *********************/
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent! as RenderBox;
     expect(tip.size.height, equals(100.0));
     expect(tip.localToGlobal(tip.size.topLeft(Offset.zero)).dy, equals(100.0));
     expect(tip.localToGlobal(tip.size.bottomRight(Offset.zero)).dy, equals(200.0));
@@ -209,7 +207,7 @@ void main() {
      *                   *
      *********************/
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent! as RenderBox;
     expect(tip.size.height, equals(100.0));
     expect(tip.localToGlobal(tip.size.topLeft(Offset.zero)).dy, equals(100.0));
     expect(tip.localToGlobal(tip.size.bottomRight(Offset.zero)).dy, equals(200.0));
@@ -280,7 +278,7 @@ void main() {
      *                   * }- 10.0 margin
      *********************/
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent! as RenderBox;
     expect(tip.size.height, equals(190.0));
     expect(tip.localToGlobal(tip.size.topLeft(Offset.zero)).dy, equals(399.0));
     expect(tip.localToGlobal(tip.size.bottomRight(Offset.zero)).dy, equals(589.0));
@@ -349,7 +347,7 @@ void main() {
      *                   * }- 10.0 margin
      *********************/
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent! as RenderBox;
     expect(tip.size.height, equals(190.0));
     expect(tip.localToGlobal(tip.size.topLeft(Offset.zero)).dy, equals(399.0));
     expect(tip.localToGlobal(tip.size.bottomRight(Offset.zero)).dy, equals(589.0));
@@ -408,7 +406,7 @@ void main() {
      *                   * }- 10.0 margin
      *********************/
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent! as RenderBox;
     expect(tip.size.height, equals(190.0));
     expect(tip.localToGlobal(tip.size.topLeft(Offset.zero)).dy, equals(400.0));
     expect(tip.localToGlobal(tip.size.bottomRight(Offset.zero)).dy, equals(590.0));
@@ -465,7 +463,7 @@ void main() {
      *                   * }- 10.0 margin
      *********************/
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent! as RenderBox;
     expect(tip.size.height, equals(190.0));
     expect(tip.localToGlobal(tip.size.topLeft(Offset.zero)).dy, equals(400.0));
     expect(tip.localToGlobal(tip.size.bottomRight(Offset.zero)).dy, equals(590.0));
@@ -505,7 +503,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent.parent.parent.parent.parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent!.parent!.parent!.parent!.parent! as RenderBox;
     final RenderBox tooltipContent = tester.renderObject(find.text(tooltipText));
 
     final Offset topLeftTipInGlobal = tip.localToGlobal(tip.size.topLeft(Offset.zero));
@@ -561,7 +559,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent.parent.parent.parent.parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent!.parent!.parent!.parent!.parent! as RenderBox;
     final RenderBox tooltipContent = tester.renderObject(find.text(tooltipText));
 
     final Offset topLeftTipInGlobal = tip.localToGlobal(tip.size.topLeft(Offset.zero));
@@ -609,7 +607,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style;
+    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style!;
     expect(textStyle.color, Colors.orange);
     expect(textStyle.fontFamily, null);
     expect(textStyle.decoration, TextDecoration.underline);
@@ -638,7 +636,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style;
+    final TextStyle textStyle = tester.widget<Text>(find.text(tooltipText)).style!;
     expect(textStyle.color, Colors.orange);
     expect(textStyle.fontFamily, null);
     expect(textStyle.decoration, TextDecoration.underline);
@@ -681,7 +679,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent.parent.parent.parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent!.parent!.parent!.parent! as RenderBox;
 
     expect(tip.size.height, equals(32.0));
     expect(tip.size.width, equals(74.0));
@@ -723,7 +721,7 @@ void main() {
     (key.currentState as dynamic).ensureTooltipVisible(); // Before using "as dynamic" in your code, see note at the top of the file.
     await tester.pump(const Duration(seconds: 2)); // faded in, show timer started (and at 0.0)
 
-    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent.parent.parent.parent as RenderBox;
+    final RenderBox tip = tester.renderObject(find.text(tooltipText)).parent!.parent!.parent!.parent! as RenderBox;
 
     expect(tip.size.height, equals(32.0));
     expect(tip.size.width, equals(74.0));
@@ -1259,6 +1257,6 @@ void main() {
 
 SemanticsNode findDebugSemantics(RenderObject object) {
   if (object.debugSemantics != null)
-    return object.debugSemantics;
-  return findDebugSemantics(object.parent as RenderObject);
+    return object.debugSemantics!;
+  return findDebugSemantics(object.parent! as RenderObject);
 }

packages/flutter/test/material/typography_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -19,16 +17,16 @@ void main() {
   });
 
   test('Typography on non-Apple platforms defaults to the correct font', () {
-    expect(Typography.material2018(platform: TargetPlatform.android).black.headline6.fontFamily, 'Roboto');
-    expect(Typography.material2018(platform: TargetPlatform.fuchsia).black.headline6.fontFamily, 'Roboto');
-    expect(Typography.material2018(platform: TargetPlatform.linux).black.headline6.fontFamily, 'Roboto');
-    expect(Typography.material2018(platform: TargetPlatform.linux).black.headline6.fontFamilyFallback, <String>['Ubuntu', 'Cantarell', 'DejaVu Sans', 'Liberation Sans', 'Arial']);
-    expect(Typography.material2018(platform: TargetPlatform.windows).black.headline6.fontFamily, 'Segoe UI');
-    expect(Typography.material2018(platform: TargetPlatform.android).white.headline6.fontFamily, 'Roboto');
-    expect(Typography.material2018(platform: TargetPlatform.fuchsia).white.headline6.fontFamily, 'Roboto');
-    expect(Typography.material2018(platform: TargetPlatform.linux).white.headline6.fontFamily, 'Roboto');
-    expect(Typography.material2018(platform: TargetPlatform.linux).white.headline6.fontFamilyFallback, <String>['Ubuntu', 'Cantarell', 'DejaVu Sans', 'Liberation Sans', 'Arial']);
-    expect(Typography.material2018(platform: TargetPlatform.windows).white.headline6.fontFamily, 'Segoe UI');
+    expect(Typography.material2018(platform: TargetPlatform.android).black.headline6!.fontFamily, 'Roboto');
+    expect(Typography.material2018(platform: TargetPlatform.fuchsia).black.headline6!.fontFamily, 'Roboto');
+    expect(Typography.material2018(platform: TargetPlatform.linux).black.headline6!.fontFamily, 'Roboto');
+    expect(Typography.material2018(platform: TargetPlatform.linux).black.headline6!.fontFamilyFallback, <String>['Ubuntu', 'Cantarell', 'DejaVu Sans', 'Liberation Sans', 'Arial']);
+    expect(Typography.material2018(platform: TargetPlatform.windows).black.headline6!.fontFamily, 'Segoe UI');
+    expect(Typography.material2018(platform: TargetPlatform.android).white.headline6!.fontFamily, 'Roboto');
+    expect(Typography.material2018(platform: TargetPlatform.fuchsia).white.headline6!.fontFamily, 'Roboto');
+    expect(Typography.material2018(platform: TargetPlatform.linux).white.headline6!.fontFamily, 'Roboto');
+    expect(Typography.material2018(platform: TargetPlatform.linux).white.headline6!.fontFamilyFallback, <String>['Ubuntu', 'Cantarell', 'DejaVu Sans', 'Liberation Sans', 'Arial']);
+    expect(Typography.material2018(platform: TargetPlatform.windows).white.headline6!.fontFamily, 'Segoe UI');
   });
 
   // Ref: https://developer.apple.com/ios/human-interface-guidelines/visual-design/typography/
@@ -91,7 +89,7 @@ void main() {
 
     final List<String> nonDefaultPropertyNames = builder.properties
       .where((DiagnosticsNode node) => !node.isFiltered(DiagnosticLevel.info))
-      .map((DiagnosticsNode node) => node.name).toList();
+      .map((DiagnosticsNode node) => node.name!).toList();
 
     expect(nonDefaultPropertyNames, <String>['black', 'white', 'englishLike', 'dense', 'tall']);
   });
@@ -106,81 +104,81 @@ void main() {
     const FontWeight medium = FontWeight.w500;
 
     // H1 Roboto light 96 -1.5
-    expect(theme.headline1.fontFamily, 'Roboto');
-    expect(theme.headline1.fontWeight, light);
-    expect(theme.headline1.fontSize, 96);
-    expect(theme.headline1.letterSpacing, -1.5);
+    expect(theme.headline1!.fontFamily, 'Roboto');
+    expect(theme.headline1!.fontWeight, light);
+    expect(theme.headline1!.fontSize, 96);
+    expect(theme.headline1!.letterSpacing, -1.5);
 
     // H2 Roboto light 60 -0.5
-    expect(theme.headline2.fontFamily, 'Roboto');
-    expect(theme.headline2.fontWeight, light);
-    expect(theme.headline2.fontSize, 60);
-    expect(theme.headline2.letterSpacing, -0.5);
+    expect(theme.headline2!.fontFamily, 'Roboto');
+    expect(theme.headline2!.fontWeight, light);
+    expect(theme.headline2!.fontSize, 60);
+    expect(theme.headline2!.letterSpacing, -0.5);
 
     // H3 Roboto regular 48 0
-    expect(theme.headline3.fontFamily, 'Roboto');
-    expect(theme.headline3.fontWeight, regular);
-    expect(theme.headline3.fontSize, 48);
-    expect(theme.headline3.letterSpacing, 0);
+    expect(theme.headline3!.fontFamily, 'Roboto');
+    expect(theme.headline3!.fontWeight, regular);
+    expect(theme.headline3!.fontSize, 48);
+    expect(theme.headline3!.letterSpacing, 0);
 
     // H4 Roboto regular 34 0.25
-    expect(theme.headline4.fontFamily, 'Roboto');
-    expect(theme.headline4.fontWeight, regular);
-    expect(theme.headline4.fontSize, 34);
-    expect(theme.headline4.letterSpacing, 0.25);
+    expect(theme.headline4!.fontFamily, 'Roboto');
+    expect(theme.headline4!.fontWeight, regular);
+    expect(theme.headline4!.fontSize, 34);
+    expect(theme.headline4!.letterSpacing, 0.25);
 
     // H5 Roboto regular 24 0
-    expect(theme.headline5.fontFamily, 'Roboto');
-    expect(theme.headline5.fontWeight, regular);
-    expect(theme.headline5.fontSize, 24);
-    expect(theme.headline5.letterSpacing, 0);
+    expect(theme.headline5!.fontFamily, 'Roboto');
+    expect(theme.headline5!.fontWeight, regular);
+    expect(theme.headline5!.fontSize, 24);
+    expect(theme.headline5!.letterSpacing, 0);
 
     // H6 Roboto medium 20 0.15
-    expect(theme.headline6.fontFamily, 'Roboto');
-    expect(theme.headline6.fontWeight, medium);
-    expect(theme.headline6.fontSize, 20);
-    expect(theme.headline6.letterSpacing, 0.15);
+    expect(theme.headline6!.fontFamily, 'Roboto');
+    expect(theme.headline6!.fontWeight, medium);
+    expect(theme.headline6!.fontSize, 20);
+    expect(theme.headline6!.letterSpacing, 0.15);
 
     // Subtitle1 Roboto regular 16 0.15
-    expect(theme.subtitle1.fontFamily, 'Roboto');
-    expect(theme.subtitle1.fontWeight, regular);
-    expect(theme.subtitle1.fontSize, 16);
-    expect(theme.subtitle1.letterSpacing, 0.15);
+    expect(theme.subtitle1!.fontFamily, 'Roboto');
+    expect(theme.subtitle1!.fontWeight, regular);
+    expect(theme.subtitle1!.fontSize, 16);
+    expect(theme.subtitle1!.letterSpacing, 0.15);
 
     // Subtitle2 Roboto medium 14 0.1
-    expect(theme.subtitle2.fontFamily, 'Roboto');
-    expect(theme.subtitle2.fontWeight, medium);
-    expect(theme.subtitle2.fontSize, 14);
-    expect(theme.subtitle2.letterSpacing, 0.1);
+    expect(theme.subtitle2!.fontFamily, 'Roboto');
+    expect(theme.subtitle2!.fontWeight, medium);
+    expect(theme.subtitle2!.fontSize, 14);
+    expect(theme.subtitle2!.letterSpacing, 0.1);
 
     // Body1 Roboto regular 16 0.5
-    expect(theme.bodyText1.fontFamily, 'Roboto');
-    expect(theme.bodyText1.fontWeight, regular);
-    expect(theme.bodyText1.fontSize, 16);
-    expect(theme.bodyText1.letterSpacing, 0.5);
+    expect(theme.bodyText1!.fontFamily, 'Roboto');
+    expect(theme.bodyText1!.fontWeight, regular);
+    expect(theme.bodyText1!.fontSize, 16);
+    expect(theme.bodyText1!.letterSpacing, 0.5);
 
     // Body2 Roboto regular 14 0.25
-    expect(theme.bodyText2.fontFamily, 'Roboto');
-    expect(theme.bodyText2.fontWeight, regular);
-    expect(theme.bodyText2.fontSize, 14);
-    expect(theme.bodyText2.letterSpacing, 0.25);
+    expect(theme.bodyText2!.fontFamily, 'Roboto');
+    expect(theme.bodyText2!.fontWeight, regular);
+    expect(theme.bodyText2!.fontSize, 14);
+    expect(theme.bodyText2!.letterSpacing, 0.25);
 
     // BUTTON Roboto medium 14 1.25
-    expect(theme.button.fontFamily, 'Roboto');
-    expect(theme.button.fontWeight, medium);
-    expect(theme.button.fontSize, 14);
-    expect(theme.button.letterSpacing, 1.25);
+    expect(theme.button!.fontFamily, 'Roboto');
+    expect(theme.button!.fontWeight, medium);
+    expect(theme.button!.fontSize, 14);
+    expect(theme.button!.letterSpacing, 1.25);
 
     // Caption Roboto regular 12 0.4
-    expect(theme.caption.fontFamily, 'Roboto');
-    expect(theme.caption.fontWeight, regular);
-    expect(theme.caption.fontSize, 12);
-    expect(theme.caption.letterSpacing, 0.4);
+    expect(theme.caption!.fontFamily, 'Roboto');
+    expect(theme.caption!.fontWeight, regular);
+    expect(theme.caption!.fontSize, 12);
+    expect(theme.caption!.letterSpacing, 0.4);
 
     // OVERLINE Roboto regular 10 1.5
-    expect(theme.overline.fontFamily, 'Roboto');
-    expect(theme.overline.fontWeight, regular);
-    expect(theme.overline.fontSize, 10);
-    expect(theme.overline.letterSpacing, 1.5);
+    expect(theme.overline!.fontFamily, 'Roboto');
+    expect(theme.overline!.fontWeight, regular);
+    expect(theme.overline!.fontSize, 10);
+    expect(theme.overline!.letterSpacing, 1.5);
   });
 }

packages/flutter/test/material/user_accounts_drawer_header_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -143,7 +141,7 @@ void main() {
 
   // Regression test for https://github.com/flutter/flutter/issues/25801.
   testWidgets('UserAccountsDrawerHeader icon does not rotate after setState', (WidgetTester tester) async {
-    StateSetter testSetState;
+    late StateSetter testSetState;
     await tester.pumpWidget(MaterialApp(
       home: Material(
         child: StatefulBuilder(
@@ -251,12 +249,12 @@ void main() {
 
   testWidgets('UserAccountsDrawerHeader null parameters LTR', (WidgetTester tester) async {
     Widget buildFrame({
-      Widget currentAccountPicture,
-      List<Widget> otherAccountsPictures,
-      Widget accountName,
-      Widget accountEmail,
-      VoidCallback onDetailsPressed,
-      EdgeInsets margin,
+      Widget? currentAccountPicture,
+      List<Widget>? otherAccountsPictures,
+      Widget? accountName,
+      Widget? accountEmail,
+      VoidCallback? onDetailsPressed,
+      EdgeInsets? margin,
     }) {
       return MaterialApp(
         home: Material(
@@ -359,12 +357,12 @@ void main() {
 
   testWidgets('UserAccountsDrawerHeader null parameters RTL', (WidgetTester tester) async {
     Widget buildFrame({
-      Widget currentAccountPicture,
-      List<Widget> otherAccountsPictures,
-      Widget accountName,
-      Widget accountEmail,
-      VoidCallback onDetailsPressed,
-      EdgeInsets margin,
+      Widget? currentAccountPicture,
+      List<Widget>? otherAccountsPictures,
+      Widget? accountName,
+      Widget? accountEmail,
+      VoidCallback? onDetailsPressed,
+      EdgeInsets? margin,
     }) {
       return MaterialApp(
         home: Directionality(

packages/flutter/test/material/will_pop_test.dart

@@ -2,21 +2,19 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 
 bool willPopValue = false;
 
 class SamplePage extends StatefulWidget {
-  const SamplePage({ Key key }) : super(key: key);
+  const SamplePage({ Key? key }) : super(key: key);
   @override
   SamplePageState createState() => SamplePageState();
 }
 
 class SamplePageState extends State<SamplePage> {
-  ModalRoute<void> _route;
+  ModalRoute<void>? _route;
 
   Future<bool> _callback() async => willPopValue;
 
@@ -45,7 +43,7 @@ class SamplePageState extends State<SamplePage> {
 int willPopCount = 0;
 
 class SampleForm extends StatelessWidget {
-  const SampleForm({ Key key, this.callback }) : super(key: key);
+  const SampleForm({ Key? key, required this.callback }) : super(key: key);
 
   final WillPopCallback callback;
 
@@ -68,7 +66,7 @@ class SampleForm extends StatelessWidget {
 
 // Expose the protected hasScopedWillPopCallback getter
 class TestPageRoute<T> extends MaterialPageRoute<T> {
-  TestPageRoute({ WidgetBuilder builder })
+  TestPageRoute({ required WidgetBuilder builder })
     : super(builder: builder, maintainState: true);
 
   bool get hasCallback => super.hasScopedWillPopCallback;
@@ -118,7 +116,7 @@ void main() {
 
     // Use didPopRoute() to simulate the system back button. Check that
     // didPopRoute() indicates that the notification was handled.
-    final dynamic widgetsAppState = tester.state(find.byType(WidgetsApp));
+    final dynamic widgetsAppState = tester.state(find.byType(WidgetsApp)); // ignore: unnecessary_nullable_for_final_variable_declarations
     expect(await widgetsAppState.didPopRoute(), isTrue);
     expect(find.text('Sample Page'), findsOneWidget);
 
@@ -141,7 +139,7 @@ void main() {
                 child: TextButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context).push(MaterialPageRoute<void>(
+                    Navigator.of(context)!.push(MaterialPageRoute<void>(
                       builder: (BuildContext context) {
                         return SampleForm(
                           callback: () => Future<bool>.value(willPopValue),
@@ -162,12 +160,6 @@ void main() {
     await tester.pumpAndSettle();
     expect(find.text('Sample Form'), findsOneWidget);
 
-    // Should not pop if callback returns null
-    willPopValue = null;
-    await tester.tap(find.byTooltip('Back'));
-    await tester.pumpAndSettle();
-    expect(find.text('Sample Form'), findsOneWidget);
-
     // Should pop if callback returns true
     willPopValue = true;
     await tester.tap(find.byTooltip('Back'));
@@ -186,7 +178,7 @@ void main() {
                 child: TextButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context).push(MaterialPageRoute<void>(
+                    Navigator.of(context)!.push(MaterialPageRoute<void>(
                       builder: (BuildContext context) {
                         return SampleForm(
                           callback: () => Future<bool>.value(willPopValue),
@@ -238,11 +230,11 @@ void main() {
             actions: <Widget> [
               TextButton(
                 child: const Text('YES'),
-                onPressed: () { Navigator.of(context).pop(true); },
+                onPressed: () { Navigator.of(context)!.pop(true); },
               ),
               TextButton(
                 child: const Text('NO'),
-                onPressed: () { Navigator.of(context).pop(false); },
+                onPressed: () { Navigator.of(context)!.pop(false); },
               ),
             ],
           );
@@ -260,7 +252,7 @@ void main() {
                 child: TextButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context).push(MaterialPageRoute<void>(
+                    Navigator.of(context)!.push(MaterialPageRoute<void>(
                       builder: (BuildContext context) {
                         return SampleForm(
                           callback: () => showYesNoAlert(context),
@@ -322,7 +314,7 @@ void main() {
   });
 
   testWidgets('Route.scopedWillPop callbacks do not accumulate', (WidgetTester tester) async {
-    StateSetter contentsSetState; // call this to rebuild the route's SampleForm contents
+    late StateSetter contentsSetState; // call this to rebuild the route's SampleForm contents
     bool contentsEmpty = false; // when true, don't include the SampleForm in the route
 
     final TestPageRoute<void> route = TestPageRoute<void>(
@@ -330,7 +322,7 @@ void main() {
         return StatefulBuilder(
           builder: (BuildContext context, StateSetter setState) {
             contentsSetState = setState;
-            return contentsEmpty ? Container() : SampleForm(key: UniqueKey());
+            return contentsEmpty ? Container() : SampleForm(key: UniqueKey(), callback: () async => false);
           }
         );
       },
@@ -346,7 +338,7 @@ void main() {
                 child: TextButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context).push(route);
+                    Navigator.of(context)!.push(route);
                   },
                 ),
               );

packages/flutter/test/widgets/app_overrides_test.dart

@@ -2,13 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 
 class TestRoute<T> extends PageRoute<T> {
-  TestRoute({ this.child, RouteSettings settings }) : super(settings: settings);
+  TestRoute({ required this.child, RouteSettings? settings }) : super(settings: settings);
 
   final Widget child;
 
@@ -16,10 +14,10 @@ class TestRoute<T> extends PageRoute<T> {
   Duration get transitionDuration => const Duration(milliseconds: 150);
 
   @override
-  Color get barrierColor => null;
+  Color? get barrierColor => null;
 
   @override
-  String get barrierLabel => null;
+  String? get barrierLabel => null;
 
   @override
   bool get maintainState => false;

packages/flutter/test/widgets/app_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
@@ -33,7 +31,7 @@ void main() {
     await tester.pumpWidget(
       WidgetsApp(
         key: key,
-        builder: (BuildContext context, Widget child) {
+        builder: (BuildContext context, Widget? child) {
           return const Placeholder();
         },
         color: const Color(0xFF123456),
@@ -43,17 +41,17 @@ void main() {
   });
 
   testWidgets('WidgetsApp can override default key bindings', (WidgetTester tester) async {
-    bool checked = false;
+    bool? checked = false;
     final GlobalKey key = GlobalKey();
     await tester.pumpWidget(
       WidgetsApp(
         key: key,
-        builder: (BuildContext context, Widget child) {
+        builder: (BuildContext context, Widget? child) {
           return Material(
             child: Checkbox(
               value: checked,
               autofocus: true,
-              onChanged: (bool value) {
+              onChanged: (bool? value) {
                 checked = value;
               },
             ),
@@ -79,12 +77,12 @@ void main() {
         shortcuts: <LogicalKeySet, Intent> {
           LogicalKeySet(LogicalKeyboardKey.space): const TestIntent(),
         },
-        builder: (BuildContext context, Widget child) {
+        builder: (BuildContext context, Widget? child) {
           return Material(
             child: Checkbox(
               value: checked,
               autofocus: true,
-              onChanged: (bool value) {
+              onChanged: (bool? value) {
                 checked = value;
               },
             ),
@@ -104,16 +102,16 @@ void main() {
   });
 
   testWidgets('WidgetsApp default activation key mappings work', (WidgetTester tester) async {
-    bool checked = false;
+    bool? checked = false;
 
     await tester.pumpWidget(
       WidgetsApp(
-        builder: (BuildContext context, Widget child) {
+        builder: (BuildContext context, Widget? child) {
           return Material(
             child: Checkbox(
               value: checked,
               autofocus: true,
-              onChanged: (bool value) {
+              onChanged: (bool? value) {
                 checked = value;
               },
             ),
@@ -147,15 +145,15 @@ void main() {
 
   group('error control test', () {
     Future<void> expectFlutterError({
-      GlobalKey<NavigatorState> key,
-      Widget widget,
-      WidgetTester tester,
-      String errorMessage,
+      required GlobalKey<NavigatorState> key,
+      required Widget widget,
+      required WidgetTester tester,
+      required String errorMessage,
     }) async {
       await tester.pumpWidget(widget);
-      FlutterError error;
+      late FlutterError error;
       try {
-        key.currentState.pushNamed('/path');
+        key.currentState!.pushNamed('/path');
       } on FlutterError catch (e) {
         error = e;
       } finally {
@@ -258,7 +256,7 @@ void main() {
     expect(find.text('non-regular page two'), findsOneWidget);
     expect(find.text('non-regular page one'), findsNothing);
     expect(find.text('regular page'), findsNothing);
-    navigatorKey.currentState.pop();
+    navigatorKey.currentState!.pop();
     await tester.pumpAndSettle();
     expect(find.text('non-regular page two'), findsNothing);
     expect(find.text('non-regular page one'), findsOneWidget);
@@ -273,7 +271,7 @@ void main() {
     );
     final SimpleNavigatorRouterDelegate delegate = SimpleNavigatorRouterDelegate(
       builder: (BuildContext context, RouteInformation information) {
-        return Text(information.location);
+        return Text(information.location!);
       },
       onPopPage: (Route<void> route, void result, SimpleNavigatorRouterDelegate delegate) {
         delegate.routeInformation = const RouteInformation(
@@ -292,7 +290,7 @@ void main() {
 
     // Simulate android back button intent.
     final ByteData message = const JSONMethodCodec().encodeMethodCall(const MethodCall('popRoute'));
-    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/navigation', message, (_) { });
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/navigation', message, (_) { });
     await tester.pumpAndSettle();
     expect(find.text('popped'), findsOneWidget);
   });
@@ -300,8 +298,9 @@ void main() {
   testWidgets('WidgetsApp.router has correct default', (WidgetTester tester) async {
     final SimpleNavigatorRouterDelegate delegate = SimpleNavigatorRouterDelegate(
       builder: (BuildContext context, RouteInformation information) {
-        return Text(information.location);
+        return Text(information.location!);
       },
+      onPopPage: (Route<Object?> route, Object? result, SimpleNavigatorRouterDelegate delegate) => true,
     );
     await tester.pumpWidget(WidgetsApp.router(
       routeInformationParser: SimpleRouteInformationParser(),
@@ -331,22 +330,22 @@ class SimpleRouteInformationParser extends RouteInformationParser<RouteInformati
 
 class SimpleNavigatorRouterDelegate extends RouterDelegate<RouteInformation> with PopNavigatorRouterDelegateMixin<RouteInformation>, ChangeNotifier {
   SimpleNavigatorRouterDelegate({
-    @required this.builder,
-    this.onPopPage,
+    required this.builder,
+    required this.onPopPage,
   });
 
   @override
   GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
 
   RouteInformation get routeInformation => _routeInformation;
-  RouteInformation _routeInformation;
+  late RouteInformation _routeInformation;
   set routeInformation(RouteInformation newValue) {
     _routeInformation = newValue;
     notifyListeners();
   }
 
-  SimpleRouterDelegateBuilder builder;
-  SimpleNavigatorRouterDelegatePopPage<void> onPopPage;
+  final SimpleRouterDelegateBuilder builder;
+  final SimpleNavigatorRouterDelegatePopPage<void> onPopPage;
 
   @override
   Future<void> setNewRoutePath(RouteInformation configuration) {
@@ -370,7 +369,7 @@ class SimpleNavigatorRouterDelegate extends RouterDelegate<RouteInformation> wit
           child: Text('base'),
         ),
         MaterialPage<void>(
-          key: ValueKey<String>(routeInformation?.location),
+          key: ValueKey<String>(routeInformation.location!),
           child: builder(context, routeInformation),
         )
       ],

packages/flutter/test/widgets/app_title_test.dart

@@ -2,15 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 
 const Color kTitleColor = Color(0xFF333333);
 const String kTitleString = 'Hello World';
 
-Future<void> pumpApp(WidgetTester tester, { GenerateAppTitle onGenerateTitle }) async {
+Future<void> pumpApp(WidgetTester tester, { GenerateAppTitle? onGenerateTitle }) async {
   await tester.pumpWidget(
     WidgetsApp(
       supportedLocales: const <Locale>[

packages/flutter/test/widgets/aspect_ratio_test.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';

packages/flutter/test/widgets/async_lifecycle_test.dart

@@ -2,13 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 class InvalidOnInitLifecycleWidget extends StatefulWidget {
-  const InvalidOnInitLifecycleWidget({Key key}) : super(key: key);
+  const InvalidOnInitLifecycleWidget({Key? key}) : super(key: key);
 
   @override
   InvalidOnInitLifecycleWidgetState createState() => InvalidOnInitLifecycleWidgetState();
@@ -27,7 +25,7 @@ class InvalidOnInitLifecycleWidgetState extends State<InvalidOnInitLifecycleWidg
 }
 
 class InvalidDidUpdateWidgetLifecycleWidget extends StatefulWidget {
-  const InvalidDidUpdateWidgetLifecycleWidget({Key key, this.id}) : super(key: key);
+  const InvalidDidUpdateWidgetLifecycleWidget({Key? key, required this.id}) : super(key: key);
 
   final int id;