Add test for animated_align.0.dart API example. (#146719)

This PR contributes to flutter/flutter#130459

### Description
- Adds `examples/api/test/widgets/implicit_animations/animated_align.0_test.dart` test

Author: ksokolovskyi

dev/bots/check_code_samples.dart

@@ -471,7 +471,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/widgets/focus_scope/focus.1_test.dart',
   'examples/api/test/widgets/focus_scope/focus_scope.0_test.dart',
   'examples/api/test/widgets/implicit_animations/animated_fractionally_sized_box.0_test.dart',
-  'examples/api/test/widgets/implicit_animations/animated_align.0_test.dart',
   'examples/api/test/widgets/implicit_animations/sliver_animated_opacity.0_test.dart',
   'examples/api/test/widgets/scroll_view/custom_scroll_view.1_test.dart',
   'examples/api/test/widgets/inherited_notifier/inherited_notifier.0_test.dart',

examples/api/lib/widgets/implicit_animations/animated_align.0.dart

@@ -11,19 +11,33 @@ void main() => runApp(const AnimatedAlignExampleApp());
 class AnimatedAlignExampleApp extends StatelessWidget {
   const AnimatedAlignExampleApp({super.key});
 
+  static const Duration duration = Duration(seconds: 1);
+  static const Curve curve = Curves.fastOutSlowIn;
+
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
       home: Scaffold(
         appBar: AppBar(title: const Text('AnimatedAlign Sample')),
-        body: const AnimatedAlignExample(),
+        body: const AnimatedAlignExample(
+          duration: duration,
+          curve: curve,
+        ),
       ),
     );
   }
 }
 
 class AnimatedAlignExample extends StatefulWidget {
-  const AnimatedAlignExample({super.key});
+  const AnimatedAlignExample({
+    required this.duration,
+    required this.curve,
+    super.key,
+  });
+
+  final Duration duration;
+
+  final Curve curve;
 
   @override
   State<AnimatedAlignExample> createState() => _AnimatedAlignExampleState();
@@ -47,8 +61,8 @@ class _AnimatedAlignExampleState extends State<AnimatedAlignExample> {
           color: Colors.red,
           child: AnimatedAlign(
             alignment: selected ? Alignment.topRight : Alignment.bottomLeft,
-            duration: const Duration(seconds: 1),
-            curve: Curves.fastOutSlowIn,
+            duration: widget.duration,
+            curve: widget.curve,
             child: const FlutterLogo(size: 50.0),
           ),
         ),

examples/api/test/widgets/implicit_animations/animated_align.0_test.dart

@@ -0,0 +1,79 @@
+// Copyright 2014 The Flutter 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/material.dart';
+import 'package:flutter_api_samples/widgets/implicit_animations/animated_align.0.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('AnimatedAlign animates on tap', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.AnimatedAlignExampleApp(),
+    );
+
+    final Finder alignFinder = find.descendant(
+      of: find.byType(AnimatedAlign),
+      matching: find.byType(Align),
+    );
+
+    const Alignment beginAlignment = Alignment.bottomLeft;
+    const Alignment endAlignment = Alignment.topRight;
+
+    Align align = tester.widget(alignFinder);
+    expect(align.alignment, beginAlignment);
+
+    // Tap on the AnimatedAlignExample to start the forward animation.
+    await tester.tap(find.byType(example.AnimatedAlignExample));
+    await tester.pump();
+
+    align = tester.widget(alignFinder);
+    expect(align.alignment, beginAlignment);
+
+    // Advance animation to the middle.
+    await tester.pump(example.AnimatedAlignExampleApp.duration ~/ 2);
+
+    align = tester.widget(alignFinder);
+    expect(
+      align.alignment,
+      Alignment.lerp(
+        beginAlignment,
+        endAlignment,
+        example.AnimatedAlignExampleApp.curve.transform(0.5),
+      ),
+    );
+
+    // Advance animation to the end.
+    await tester.pump(example.AnimatedAlignExampleApp.duration ~/ 2);
+
+    align = tester.widget(alignFinder);
+    expect(align.alignment, endAlignment);
+
+    // Tap on the AnimatedAlignExample again to start the reverse animation.
+    await tester.tap(find.byType(example.AnimatedAlignExample));
+    await tester.pump();
+
+    align = tester.widget(alignFinder);
+    expect(align.alignment, endAlignment);
+
+    // Advance animation to the middle.
+    await tester.pump(example.AnimatedAlignExampleApp.duration ~/ 2);
+
+    align = tester.widget(alignFinder);
+    expect(
+      align.alignment,
+      Alignment.lerp(
+        endAlignment,
+        beginAlignment,
+        example.AnimatedAlignExampleApp.curve.transform(0.5),
+      ),
+    );
+
+    // Advance animation to the end.
+    await tester.pump(example.AnimatedAlignExampleApp.duration ~/ 2);
+
+    align = tester.widget(alignFinder);
+    expect(align.alignment, beginAlignment);
+  });
+}