Adds `CommonFinders.bySubtype<T extends Widget>()` finder. (#91415)

packages/flutter_test/lib/src/finders.dart

@@ -128,6 +128,24 @@ class CommonFinders {
   /// nodes that are [Offstage] or that are from inactive [Route]s.
   Finder byKey(Key key, { bool skipOffstage = true }) => _KeyFinder(key, skipOffstage: skipOffstage);
 
+  /// Finds widgets by searching for widgets implementing a particular type.
+  ///
+  /// This matcher accepts subtypes. For example a
+  /// `bySubtype<StatefulWidget>()` will find any stateful widget.
+  ///
+  /// ## Sample code
+  ///
+  /// ```dart
+  /// expect(find.bySubtype<IconButton>(), findsOneWidget);
+  /// ```
+  ///
+  /// If the `skipOffstage` argument is true (the default), then this skips
+  /// nodes that are [Offstage] or that are from inactive [Route]s.
+  ///
+  /// See also:
+  /// * [byType], which does not do subtype tests.
+  Finder bySubtype<T extends Widget>({ bool skipOffstage = true }) => _WidgetSubtypeFinder<T>(skipOffstage: skipOffstage);
+
   /// Finds widgets by searching for widgets with a particular type.
   ///
   /// This does not do subclass tests, so for example
@@ -144,6 +162,9 @@ class CommonFinders {
   ///
   /// If the `skipOffstage` argument is true (the default), then this skips
   /// nodes that are [Offstage] or that are from inactive [Route]s.
+  ///
+  /// See also:
+  /// * [bySubtype], which allows subtype tests.
   Finder byType(Type type, { bool skipOffstage = true }) => _WidgetTypeFinder(type, skipOffstage: skipOffstage);
 
   /// Finds [Icon] widgets containing icon data equal to the `icon`
@@ -713,6 +734,18 @@ class _KeyFinder extends MatchFinder {
   }
 }
 
+class _WidgetSubtypeFinder<T extends Widget> extends MatchFinder {
+  _WidgetSubtypeFinder({ bool skipOffstage = true }) : super(skipOffstage: skipOffstage);
+
+  @override
+  String get description => 'is "$T"';
+
+  @override
+  bool matches(Element candidate) {
+    return candidate.widget is T;
+  }
+}
+
 class _WidgetTypeFinder extends MatchFinder {
   _WidgetTypeFinder(this.widgetType, { bool skipOffstage = true }) : super(skipOffstage: skipOffstage);
 

packages/flutter_test/test/finders_test.dart

@@ -11,17 +11,18 @@ import 'package:flutter_test/flutter_test.dart';
 void main() {
   group('image', () {
     testWidgets('finds Image widgets', (WidgetTester tester) async {
-      await tester.pumpWidget(_boilerplate(
-          Image(image: FileImage(File('test')))
-      ));
+      await tester
+          .pumpWidget(_boilerplate(Image(image: FileImage(File('test')))));
       expect(find.image(FileImage(File('test'))), findsOneWidget);
     });
 
     testWidgets('finds Button widgets with Image', (WidgetTester tester) async {
-      await tester.pumpWidget(_boilerplate(
-          ElevatedButton(onPressed: null, child: Image(image: FileImage(File('test'))),)
-      ));
-      expect(find.widgetWithImage(ElevatedButton, FileImage(File('test'))), findsOneWidget);
+      await tester.pumpWidget(_boilerplate(ElevatedButton(
+        onPressed: null,
+        child: Image(image: FileImage(File('test'))),
+      )));
+      expect(find.widgetWithImage(ElevatedButton, FileImage(File('test'))),
+          findsOneWidget);
     });
   });
 
@@ -34,9 +35,10 @@ void main() {
     });
 
     testWidgets('finds Text.rich widgets', (WidgetTester tester) async {
-      await tester.pumpWidget(_boilerplate(
-        const Text.rich(
-          TextSpan(text: 't', children: <TextSpan>[
+      await tester.pumpWidget(_boilerplate(const Text.rich(
+        TextSpan(
+          text: 't',
+          children: <TextSpan>[
             TextSpan(text: 'e'),
             TextSpan(text: 'st'),
           ],
@@ -137,9 +139,10 @@ void main() {
     });
 
     testWidgets('finds Text.rich widgets', (WidgetTester tester) async {
-      await tester.pumpWidget(_boilerplate(
-          const Text.rich(
-            TextSpan(text: 'this', children: <TextSpan>[
+      await tester.pumpWidget(_boilerplate(const Text.rich(
+        TextSpan(
+          text: 'this',
+          children: <TextSpan>[
             TextSpan(text: 'is'),
             TextSpan(text: 'a'),
             TextSpan(text: 'test'),
@@ -166,11 +169,13 @@ void main() {
   });
 
   group('semantics', () {
-    testWidgets('Throws StateError if semantics are not enabled', (WidgetTester tester) async {
+    testWidgets('Throws StateError if semantics are not enabled',
+        (WidgetTester tester) async {
       expect(() => find.bySemanticsLabel('Add'), throwsStateError);
     }, semanticsEnabled: false);
 
-    testWidgets('finds Semantically labeled widgets', (WidgetTester tester) async {
+    testWidgets('finds Semantically labeled widgets',
+        (WidgetTester tester) async {
       final SemanticsHandle semanticsHandle = tester.ensureSemantics();
       await tester.pumpWidget(_boilerplate(
         Semantics(
@@ -186,7 +191,8 @@ void main() {
       semanticsHandle.dispose();
     });
 
-    testWidgets('finds Semantically labeled widgets by RegExp', (WidgetTester tester) async {
+    testWidgets('finds Semantically labeled widgets by RegExp',
+        (WidgetTester tester) async {
       final SemanticsHandle semanticsHandle = tester.ensureSemantics();
       await tester.pumpWidget(_boilerplate(
         Semantics(
@@ -202,18 +208,19 @@ void main() {
       semanticsHandle.dispose();
     });
 
-    testWidgets('finds Semantically labeled widgets without explicit Semantics', (WidgetTester tester) async {
+    testWidgets('finds Semantically labeled widgets without explicit Semantics',
+        (WidgetTester tester) async {
       final SemanticsHandle semanticsHandle = tester.ensureSemantics();
-      await tester.pumpWidget(_boilerplate(
-        const SimpleCustomSemanticsWidget('Foo')
-      ));
+      await tester
+          .pumpWidget(_boilerplate(const SimpleCustomSemanticsWidget('Foo')));
       expect(find.bySemanticsLabel('Foo'), findsOneWidget);
       semanticsHandle.dispose();
     });
   });
 
   group('hitTestable', () {
-    testWidgets('excludes non-hit-testable widgets', (WidgetTester tester) async {
+    testWidgets('excludes non-hit-testable widgets',
+        (WidgetTester tester) async {
       await tester.pumpWidget(
         _boilerplate(IndexedStack(
           sizing: StackFit.expand,
@@ -221,13 +228,13 @@ void main() {
             GestureDetector(
               key: const ValueKey<int>(0),
               behavior: HitTestBehavior.opaque,
-              onTap: () { },
+              onTap: () {},
               child: const SizedBox.expand(),
             ),
             GestureDetector(
               key: const ValueKey<int>(1),
               behavior: HitTestBehavior.opaque,
-              onTap: () { },
+              onTap: () {},
               child: const SizedBox.expand(),
             ),
           ],
@@ -258,13 +265,52 @@ void main() {
     // candidates, it should find 1 instead of 2. If the _LastFinder wasn't
     // correctly chained after the descendant's candidates, the last element
     // with a Text widget would have been 2.
-    final Text text = find.descendant(
+    final Text text = find
+        .descendant(
           of: find.byKey(key1),
           matching: find.byType(Text),
-    ).last.evaluate().single.widget as Text;
+        )
+        .last
+        .evaluate()
+        .single
+        .widget as Text;
 
     expect(text.data, '1');
   });
+
+  testWidgets('finds multiple subtypes', (WidgetTester tester) async {
+    await tester.pumpWidget(_boilerplate(
+      Row(children: <Widget>[
+        Column(children: const <Widget>[
+          Text('Hello'),
+          Text('World'),
+        ]),
+        Column(children: <Widget>[
+          Image(image: FileImage(File('test'))),
+        ]),
+        Column(children: const <Widget>[
+          SimpleGenericWidget<int>(child: Text('one')),
+          SimpleGenericWidget<double>(child: Text('pi')),
+          SimpleGenericWidget<String>(child: Text('two')),
+        ]),
+      ]),
+    ));
+
+    expect(find.bySubtype<Row>(), findsOneWidget);
+    expect(find.bySubtype<Column>(), findsNWidgets(3));
+    // Finds both rows and columns.
+    expect(find.bySubtype<Flex>(), findsNWidgets(4));
+
+    // Finds only the requested generic subtypes.
+    expect(find.bySubtype<SimpleGenericWidget<int>>(), findsOneWidget);
+    expect(find.bySubtype<SimpleGenericWidget<num>>(), findsNWidgets(2));
+    expect(find.bySubtype<SimpleGenericWidget<Object>>(), findsNWidgets(3));
+
+    // Finds all widgets.
+    final int totalWidgetCount =
+        find.byWidgetPredicate((_) => true).evaluate().length;
+    expect(find.bySubtype<Widget>(), findsNWidgets(totalWidgetCount));
+  });
 }
 
 Widget _boilerplate(Widget child) {
@@ -280,7 +326,8 @@ class SimpleCustomSemanticsWidget extends LeafRenderObjectWidget {
   final String label;
 
   @override
-  RenderObject createRenderObject(BuildContext context) => SimpleCustomSemanticsRenderObject(label);
+  RenderObject createRenderObject(BuildContext context) =>
+      SimpleCustomSemanticsRenderObject(label);
 }
 
 class SimpleCustomSemanticsRenderObject extends RenderBox {
@@ -299,6 +346,21 @@ class SimpleCustomSemanticsRenderObject extends RenderBox {
   @override
   void describeSemanticsConfiguration(SemanticsConfiguration config) {
     super.describeSemanticsConfiguration(config);
-    config..label = label..textDirection = TextDirection.ltr;
+    config
+      ..label = label
+      ..textDirection = TextDirection.ltr;
+  }
+}
+
+class SimpleGenericWidget<T> extends StatelessWidget {
+  const SimpleGenericWidget({required Widget child, Key? key})
+      : _child = child,
+        super(key: key);
+
+  final Widget _child;
+
+  @override
+  Widget build(BuildContext context) {
+    return _child;
   }
 }