Fix train hopping animation status listeners (#178372)

Fixes https://github.com/flutter/flutter/issues/178336

### Description

- Fixes `TrainHoppingAnimation` to notify status listeners when `status`
changes
- Adds tests

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there for submitting PRs.
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we expect every widget to implement].
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above.
- [ ] I updated/added relevant documentation (doc comments with `///`).
- [X] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [X] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [X] All existing and new tests are passing.

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packages/flutter/lib/src/animation/animations.dart

@@ -543,7 +543,7 @@ class TrainHoppingAnimation extends Animation<double>
   void _statusChangeHandler(AnimationStatus status) {
     assert(_currentTrain != null);
     if (status != _lastStatus) {
-      notifyListeners();
+      notifyStatusListeners(status);
       _lastStatus = status;
     }
     assert(_lastStatus != null);

packages/flutter/test/animation/animations_test.dart

@@ -99,7 +99,9 @@ void main() {
 
   test('TrainHoppingAnimation', () {
     final AnimationController currentTrain = AnimationController(vsync: const TestVSync());
+    addTearDown(currentTrain.dispose);
     final AnimationController nextTrain = AnimationController(vsync: const TestVSync());
+    addTearDown(nextTrain.dispose);
     currentTrain.value = 0.5;
     nextTrain.value = 0.75;
     bool didSwitchTrains = false;
@@ -133,6 +135,32 @@ void main() {
     );
   });
 
+  // Regression test for https://github.com/flutter/flutter/issues/178336.
+  test('TrainHoppingAnimation notifies status listeners', () {
+    final AnimationController controller = AnimationController(
+      duration: const Duration(milliseconds: 100),
+      vsync: const TestVSync(),
+    );
+    addTearDown(controller.dispose);
+
+    final TrainHoppingAnimation animation = TrainHoppingAnimation(
+      Tween<double>(begin: 1.0, end: -1.0).animate(controller),
+      Tween<double>(begin: -1.0, end: 1.0).animate(controller),
+    );
+    addTearDown(animation.dispose);
+
+    final List<AnimationStatus> statusLog = <AnimationStatus>[];
+    animation.addStatusListener(statusLog.add);
+    expect(statusLog, isEmpty);
+
+    controller.forward();
+    expect(statusLog, equals(<AnimationStatus>[AnimationStatus.forward]));
+    statusLog.clear();
+
+    controller.reverse();
+    expect(statusLog, equals(<AnimationStatus>[AnimationStatus.dismissed]));
+  });
+
   test('AnimationMean control test', () {
     final AnimationController left = AnimationController(value: 0.5, vsync: const TestVSync());
     final AnimationController right = AnimationController(vsync: const TestVSync());