[animations]: added test for AnimatedList (#637)

animations/test/misc/animated_list_test.dart

@@ -0,0 +1,138 @@
+// 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/animated_list.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+Widget createAnimatedListDemoScreen() => MaterialApp(
+      home: AnimatedListDemo(),
+    );
+
+void main() {
+  group('Animated List Tests', () {
+    testWidgets('Initial length of list', (tester) async {
+      await tester.pumpWidget(createAnimatedListDemoScreen());
+
+      // Get the initial length of list.
+      var initialLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // Initial length of list should be equal to 5.
+      expect(
+        initialLength,
+        equals(5),
+      );
+    });
+
+    testWidgets('Length of list increases on Add Icon Button tap',
+        (tester) async {
+      await tester.pumpWidget(createAnimatedListDemoScreen());
+
+      // Get the initial length of list.
+      var initialLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // Tap on the Add Icon Button.
+      await tester.tap(find.byIcon(Icons.add));
+      await tester.pumpAndSettle();
+
+      // Get the new length of list.
+      var newLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // New length should be greater than initial length by one.
+      expect(
+        newLength,
+        equals(initialLength + 1),
+      );
+    });
+
+    testWidgets(
+        'Length of list decreases on Delete Icon Button tap at middle index',
+        (tester) async {
+      await tester.pumpWidget(createAnimatedListDemoScreen());
+
+      // Get the initial length of list.
+      var initialLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // Tap on the Delete Icon Button at middle index.
+      await tester.tap(find.byIcon(Icons.delete).at(initialLength ~/ 2));
+      await tester.pumpAndSettle();
+
+      // Get the new length of list.
+      var newLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // New length should be less than initial length by one.
+      expect(
+        newLength,
+        equals(initialLength - 1),
+      );
+    });
+
+    testWidgets(
+        'Length of list decreases on Delete Icon Button tap at start index',
+        (tester) async {
+      await tester.pumpWidget(createAnimatedListDemoScreen());
+
+      // Get the initial length of list.
+      var initialLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // Tap on the Delete Icon Button at start index.
+      await tester.tap(find.byIcon(Icons.delete).at(0));
+      await tester.pumpAndSettle();
+
+      // Get the new length of list.
+      var newLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // New length should be less than initial length by one.
+      expect(
+        newLength,
+        equals(initialLength - 1),
+      );
+    });
+
+    testWidgets(
+        'Length of list decreases on Delete Icon Button tap at end index',
+        (tester) async {
+      await tester.pumpWidget(createAnimatedListDemoScreen());
+
+      // Get the initial length of list.
+      var initialLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // Tap on the Delete Icon Button at end index.
+      await tester.tap(find.byIcon(Icons.delete).at(initialLength - 1));
+      await tester.pumpAndSettle();
+
+      // Get the new length of list.
+      var newLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // New Length should be less than initial length by one.
+      expect(
+        newLength,
+        equals(initialLength - 1),
+      );
+    });
+
+    testWidgets('All ListTiles deleted', (tester) async {
+      await tester.pumpWidget(createAnimatedListDemoScreen());
+
+      // Get the initial length of list.
+      var initialLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // Iterating over all the Delete Icon Buttons.
+      for (var i = 0; i < initialLength; i++) {
+        // Tap on the Delete Icon
+        await tester.tap(find.byIcon(Icons.delete).first);
+        await tester.pumpAndSettle();
+      }
+
+      // Get the final length of list.
+      var finalLength = tester.widgetList(find.byType(ListTile)).length;
+
+      // New length should be zero.
+      expect(
+        finalLength,
+        equals(0),
+      );
+    });
+  });
+}