Adding tests for animationStatus (#11520)

* Adding tests for animationStatus

* remove comments

* animateTo is allways forward

* clearify docs

* review comments

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

@@ -270,6 +270,10 @@ class AnimationController extends Animation<double>
   /// The most recently returned [TickerFuture], if any, is marked as having been
   /// canceled, meaning the future never completes and its [TickerFuture.orCancel]
   /// derivative future completes with a [TickerCanceled] error.
+  ///
+  /// During the animation, [status] is reported as [AnimationStatus.forward],
+  /// which switches to [AnimationStatus.completed] when [upperBound] is
+  /// reached at the end of the animation.
   TickerFuture forward({ double from }) {
     assert(() {
       if (duration == null) {
@@ -284,7 +288,7 @@ class AnimationController extends Animation<double>
     _direction = _AnimationDirection.forward;
     if (from != null)
       value = from;
-    return animateTo(upperBound);
+    return _animateToInternal(upperBound);
   }
 
   /// Starts running this animation in reverse (towards the beginning).
@@ -294,6 +298,10 @@ class AnimationController extends Animation<double>
   /// The most recently returned [TickerFuture], if any, is marked as having been
   /// canceled, meaning the future never completes and its [TickerFuture.orCancel]
   /// derivative future completes with a [TickerCanceled] error.
+  ///
+  /// During the animation, [status] is reported as [AnimationStatus.reverse],
+  /// which switches to [AnimationStatus.dismissed] when [lowerBound] is
+  /// reached at the end of the animation.
   TickerFuture reverse({ double from }) {
     assert(() {
       if (duration == null) {
@@ -308,7 +316,7 @@ class AnimationController extends Animation<double>
     _direction = _AnimationDirection.reverse;
     if (from != null)
       value = from;
-    return animateTo(lowerBound);
+    return _animateToInternal(lowerBound);
   }
 
   /// Drives the animation from its current value to target.
@@ -318,7 +326,17 @@ class AnimationController extends Animation<double>
   /// The most recently returned [TickerFuture], if any, is marked as having been
   /// canceled, meaning the future never completes and its [TickerFuture.orCancel]
   /// derivative future completes with a [TickerCanceled] error.
+  ///
+  /// During the animation, [status] is reported as [AnimationStatus.forward]
+  /// regardless of whether `target` > [value] or not. At the end of the
+  /// animation, when `target` is reached, [status] is reported as
+  /// [AnimationStatus.completed].
   TickerFuture animateTo(double target, { Duration duration, Curve curve: Curves.linear }) {
+    _direction = _AnimationDirection.forward;
+    return _animateToInternal(target, duration: duration, curve: curve);
+  }
+
+  TickerFuture _animateToInternal(double target, { Duration duration, Curve curve: Curves.linear }) {
     Duration simulationDuration = duration;
     if (simulationDuration == null) {
       assert(() {

packages/flutter/test/animation/animation_controller_test.dart

@@ -379,7 +379,7 @@ void main() {
 
     final double currentValue = controller.value;
     controller.animateTo(currentValue, duration: const Duration(milliseconds: 100));
-    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.reverse, AnimationStatus.dismissed ]));
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.reverse, AnimationStatus.completed ]));
     expect(controller.value, currentValue);
   });
 
@@ -395,4 +395,134 @@ void main() {
     expect(SchedulerBinding.instance.transientCallbackCount, equals(0), reason: 'Expected no animation.');
     expect(controller.value, 1.0);
   });
+
+  test('setting value directly sets correct status', () {
+    final AnimationController controller = new AnimationController(
+      value: 0.0,
+      lowerBound: 0.0,
+      upperBound: 1.0,
+      vsync: const TestVSync(),
+    );
+
+    expect(controller.value, 0.0);
+    expect(controller.status, AnimationStatus.dismissed);
+
+    controller.value = 0.5;
+    expect(controller.value, 0.5);
+    expect(controller.status, AnimationStatus.forward);
+
+    controller.value = 1.0;
+    expect(controller.value, 1.0);
+    expect(controller.status, AnimationStatus.completed);
+
+    controller.value = 0.5;
+    expect(controller.value, 0.5);
+    expect(controller.status, AnimationStatus.forward);
+
+    controller.value = 0.0;
+    expect(controller.value, 0.0);
+    expect(controller.status, AnimationStatus.dismissed);
+  });
+
+  test('animateTo sets correct status', () {
+    final List<AnimationStatus> statusLog = <AnimationStatus>[];
+    final AnimationController controller = new AnimationController(
+      duration: const Duration(milliseconds: 100),
+      value: 0.0,
+      lowerBound: 0.0,
+      upperBound: 1.0,
+      vsync: const TestVSync(),
+    )..addStatusListener(statusLog.add);
+
+    expect(controller.value, 0.0);
+    expect(controller.status, AnimationStatus.dismissed);
+
+    // Animate from 0.0 to 0.5
+    controller.animateTo(0.5);
+    tick(const Duration(milliseconds: 0));
+    tick(const Duration(milliseconds: 150));
+    expect(controller.value, 0.5);
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.forward, AnimationStatus.completed ]));
+    statusLog.clear();
+
+    // Animate from 0.5 to 1.0
+    controller.animateTo(1.0);
+    tick(const Duration(milliseconds: 0));
+    tick(const Duration(milliseconds: 150));
+    expect(controller.value, 1.0);
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.forward, AnimationStatus.completed ]));
+    statusLog.clear();
+
+    // Animate from 1.0 to 0.5
+    controller.animateTo(0.5);
+    tick(const Duration(milliseconds: 0));
+    tick(const Duration(milliseconds: 150));
+    expect(controller.value, 0.5);
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.forward, AnimationStatus.completed ]));
+    statusLog.clear();
+
+    // Animate from 0.5 to 1.0
+    controller.animateTo(0.0);
+    tick(const Duration(milliseconds: 0));
+    tick(const Duration(milliseconds: 150));
+    expect(controller.value, 0.0);
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.forward, AnimationStatus.completed ]));
+    statusLog.clear();
+  });
+
+  test('after a reverse call animateTo sets correct status', () {
+    final List<AnimationStatus> statusLog = <AnimationStatus>[];
+    final AnimationController controller = new AnimationController(
+      duration: const Duration(milliseconds: 100),
+      value: 1.0,
+      lowerBound: 0.0,
+      upperBound: 1.0,
+      vsync: const TestVSync(),
+    )..addStatusListener(statusLog.add);
+
+    expect(controller.value, 1.0);
+    expect(controller.status, AnimationStatus.completed);
+
+    controller.reverse();
+    tick(const Duration(milliseconds: 0));
+    tick(const Duration(milliseconds: 150));
+    expect(controller.value, 0.0);
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.reverse, AnimationStatus.dismissed ]));
+    statusLog.clear();
+
+    controller.animateTo(0.5);
+    tick(const Duration(milliseconds: 0));
+    tick(const Duration(milliseconds: 150));
+    expect(controller.value, 0.5);
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.forward, AnimationStatus.completed ]));
+    statusLog.clear();
+  });
+
+  test('after a forward call animateTo sets correct status', () {
+    final List<AnimationStatus> statusLog = <AnimationStatus>[];
+    final AnimationController controller = new AnimationController(
+      duration: const Duration(milliseconds: 100),
+      value: 0.0,
+      lowerBound: 0.0,
+      upperBound: 1.0,
+      vsync: const TestVSync(),
+    )..addStatusListener(statusLog.add);
+
+    expect(controller.value, 0.0);
+    expect(controller.status, AnimationStatus.dismissed);
+
+    controller.forward();
+    tick(const Duration(milliseconds: 0));
+    tick(const Duration(milliseconds: 150));
+    expect(controller.value, 1.0);
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.forward, AnimationStatus.completed ]));
+    statusLog.clear();
+
+    controller.animateTo(0.5);
+    tick(const Duration(milliseconds: 0));
+    tick(const Duration(milliseconds: 150));
+    expect(controller.value, 0.5);
+    expect(statusLog, equals(<AnimationStatus>[ AnimationStatus.forward, AnimationStatus.completed ]));
+    statusLog.clear();
+  });
 }