WidgetController.pump use optional duration (#62091)

packages/flutter_test/lib/src/controller.dart

@@ -423,7 +423,11 @@ abstract class WidgetController {
   /// See [PointerEventRecord].
   Future<List<Duration>> handlePointerEventRecord(List<PointerEventRecord> records);
 
-  /// Called to indicate that time should advance.
+  /// Called to indicate that there should be a new frame after an optional
+  /// delay.
+  ///
+  /// The frame is pumped after a delay of [duration] if [duration] is not null,
+  /// or immediately otherwise.
   ///
   /// This is invoked by [flingFrom], for instance, so that the sequence of
   /// pointer events occurs over time.
@@ -432,7 +436,7 @@ abstract class WidgetController {
   ///
   /// See also [SchedulerBinding.endOfFrame], which returns a future that could
   /// be appropriate to return in the implementation of this method.
-  Future<void> pump(Duration duration);
+  Future<void> pump([Duration duration]);
 
   /// Attempts to drag the given widget by the given offset, by
   /// starting a drag in the middle of the widget.
@@ -755,7 +759,7 @@ class LiveWidgetController extends WidgetController {
   LiveWidgetController(WidgetsBinding binding) : super(binding);
 
   @override
-  Future<void> pump(Duration duration) async {
+  Future<void> pump([Duration duration]) async {
     if (duration != null)
       await Future<void>.delayed(duration);
     binding.scheduleFrame();

packages/flutter_test/test/live_widget_controller_test.dart

@@ -9,7 +9,41 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-Future<void> main() async {
+class CountButton extends StatefulWidget {
+  @override
+  _CountButtonState createState() => _CountButtonState();
+}
+
+class _CountButtonState extends State<CountButton> {
+  int counter = 0;
+  @override
+  Widget build(BuildContext context) {
+    return RaisedButton(
+      child: Text('Counter $counter'),
+      onPressed: () {
+        setState(() {
+          counter += 1;
+        });
+      },
+    );
+  }
+}
+
+void main() {
+  test('Test pump on LiveWidgetController', () async {
+    runApp(MaterialApp(home: Center(child: CountButton())));
+
+    await SchedulerBinding.instance.endOfFrame;
+    final WidgetController controller =
+        LiveWidgetController(WidgetsBinding.instance);
+    await controller.tap(find.text('Counter 0'));
+    expect(find.text('Counter 0'), findsOneWidget);
+    expect(find.text('Counter 1'), findsNothing);
+    await controller.pump();
+    expect(find.text('Counter 0'), findsNothing);
+    expect(find.text('Counter 1'), findsOneWidget);
+  });
+
   test('Input event array on LiveWidgetController', () async {
     final List<String> logs = <String>[];
     runApp(