[animations] added test for HeroAnimation (#620)

animations/test/misc/hero_animation_test.dart

@@ -0,0 +1,91 @@
+// Copyright 2020 The Flutter team. 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:animations/src/misc/hero_animation.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+Widget createHeroAnimationDemoScreen() => MaterialApp(
+      home: HeroAnimationDemo(),
+    );
+
+void main() {
+  group('Hero Animation Tests', () {
+    testWidgets('Size of Container changes on Tap', (tester) async {
+      await tester.pumpWidget(createHeroAnimationDemoScreen());
+
+      // Get the initial Container.
+      var initialContainer = tester.firstWidget(find.byType(Container));
+
+      // Get the size of initial Container.
+      var initialSize = tester.getSize(find.byWidget(initialContainer));
+
+      // Tap on the Gesture Detector.
+      await tester.tap(find.byType(GestureDetector));
+      await tester.pumpAndSettle();
+
+      // Get the final Container.
+      var finalContainer = tester.firstWidget(find.byType(Container));
+
+      // Get the size of final Container.
+      var finalSize = tester.getSize(find.byWidget(finalContainer));
+
+      // initialSize should be less than finalSize.
+      expect(
+        initialSize,
+        lessThan(finalSize),
+      );
+    });
+
+    testWidgets('Color of Container changes on Tap', (tester) async {
+      await tester.pumpWidget(createHeroAnimationDemoScreen());
+
+      // Get the initial Container.
+      final initialContainer =
+          tester.firstWidget(find.byType(Container)) as Container;
+
+      // Initial color should be Color.grey[300].
+      expect(
+        (initialContainer.decoration as BoxDecoration).color,
+        Colors.grey[300],
+      );
+
+      // Tap on the GestureDetector.
+      await tester.tap(find.byType(GestureDetector));
+      await tester.pumpAndSettle();
+
+      // Get the final Container.
+      final finalContainer =
+          tester.firstWidget(find.byType(Container)) as Container;
+
+      // Final color should not be same as initial color.
+      expect(
+        (finalContainer.decoration as BoxDecoration).color,
+        isNot(
+          equals((initialContainer.decoration as BoxDecoration).color),
+        ),
+      );
+    });
+
+    testWidgets('Screen Changes on Tap', (tester) async {
+      await tester.pumpWidget(createHeroAnimationDemoScreen());
+
+      // Get the initial Screen.
+      final initialScreen = tester.firstWidget(find.byType(HeroAnimationDemo));
+
+      // Tap on the GestureDetector.
+      await tester.tap(find.byType(GestureDetector));
+      await tester.pumpAndSettle();
+
+      // Get the screen after navigation.
+      final finalScreen = tester.firstWidget(find.byType(HeroPage));
+
+      // initialScreen should not be same as finalScreen.
+      expect(
+        initialScreen,
+        isNot(equals(finalScreen)),
+      );
+    });
+  });
+}