Test all but one line in animation.dart (#4751)

The one line we don't test is the private constructor for the Curves class,
which exists to ensure that no one constructs the Curves class.

packages/flutter/test/animation/curves_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:math' as math;
+
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/animation.dart';
 import 'package:flutter/widgets.dart';
@@ -31,4 +33,62 @@ void main() {
     expect(step.transform(0.26), 1.0);
     expect(step.transform(1.0), 1.0);
   });
+
+  void expectStaysInBounds(Curve curve) {
+    expect(curve.transform(0.0), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.1), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.2), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.3), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.4), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.5), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.6), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.7), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.8), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(0.9), inInclusiveRange(0.0, 1.0));
+    expect(curve.transform(1.0), inInclusiveRange(0.0, 1.0));
+  }
+
+  test('Bounce stays in bounds', () {
+    expectStaysInBounds(Curves.bounceIn);
+    expectStaysInBounds(Curves.bounceOut);
+    expectStaysInBounds(Curves.bounceInOut);
+  });
+
+  List<double> estimateBounds(Curve curve) {
+    List<double> values = <double>[];
+
+    values.add(curve.transform(0.0));
+    values.add(curve.transform(0.1));
+    values.add(curve.transform(0.2));
+    values.add(curve.transform(0.3));
+    values.add(curve.transform(0.4));
+    values.add(curve.transform(0.5));
+    values.add(curve.transform(0.6));
+    values.add(curve.transform(0.7));
+    values.add(curve.transform(0.8));
+    values.add(curve.transform(0.9));
+    values.add(curve.transform(1.0));
+
+    return <double>[
+      values.reduce(math.min),
+      values.reduce(math.max),
+    ];
+  }
+
+  test('Ellastic overshoots its bounds', () {
+    expect(Curves.elasticIn, hasOneLineDescription);
+    expect(Curves.elasticOut, hasOneLineDescription);
+    expect(Curves.elasticInOut, hasOneLineDescription);
+
+    List<double> bounds;
+    bounds = estimateBounds(Curves.elasticIn);
+    expect(bounds[0], lessThan(0.0));
+    expect(bounds[1], lessThanOrEqualTo(1.0));
+    bounds = estimateBounds(Curves.elasticOut);
+    expect(bounds[0], greaterThanOrEqualTo(0.0));
+    expect(bounds[1], greaterThan(1.0));
+    bounds = estimateBounds(Curves.elasticInOut);
+    expect(bounds[0], lessThan(0.0));
+    expect(bounds[1], greaterThan(1.0));
+  });
 }

packages/flutter/test/animation/forces_test.dart

@@ -0,0 +1,16 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/animation.dart';
+import 'package:flutter/widgets.dart';
+
+void main() {
+  test('copyWith defaults to unchanged values', () {
+    SpringForce force = kDefaultSpringForce.copyWith();
+    expect(force.spring, kDefaultSpringForce.spring);
+    expect(force.left, kDefaultSpringForce.left);
+    expect(force.right, kDefaultSpringForce.right);
+  });
+}

packages/flutter/test/animation/tween_test.dart

@@ -0,0 +1,40 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/animation.dart';
+import 'package:flutter/widgets.dart';
+
+void main() {
+  test('Can chain tweens', () {
+    Tween<double> tween = new Tween<double>(begin: 0.30, end: 0.50);
+    expect(tween, hasOneLineDescription);
+    Animatable<double> chain = tween.chain(new Tween<double>(begin: 0.50, end: 1.0));
+    AnimationController controller = new AnimationController();
+    expect(chain.evaluate(controller), 0.40);
+    expect(chain, hasOneLineDescription);
+  });
+
+  test('Can animated tweens', () {
+    Tween<double> tween = new Tween<double>(begin: 0.30, end: 0.50);
+    AnimationController controller = new AnimationController();
+    Animation<double> animation = tween.animate(controller);
+    controller.value = 0.50;
+    expect(animation.value, 0.40);
+    expect(animation, hasOneLineDescription);
+    expect(animation.toStringDetails(), hasOneLineDescription);
+  });
+
+  test('SizeTween', () {
+    SizeTween tween = new SizeTween(begin: Size.zero, end: new Size(20.0, 30.0));
+    expect(tween.lerp(0.5), equals(new Size(10.0, 15.0)));
+    expect(tween, hasOneLineDescription);
+  });
+
+  test('IntTween', () {
+    IntTween tween = new IntTween(begin: 5, end: 9);
+    expect(tween.lerp(0.5), 7);
+    expect(tween.lerp(0.7), 8);
+  });
+}