Explain Flutter testing strategies.

Flutter testing strategies:\n\n**Test types:**\n• Unit tests - Test individual functions/classes\n• Widget tests - Test widget behavior\n• Integration tests - Test complete app flow\n\n**Unit testing:**\n\nimport 'package:flutter_test/flutter_test.dart';\n\nvoid main() {\n group('Calculator', () {\n test('should add two numbers', () {\n final calculator = Calculator();\n expect(calculator.add(2, 3), equals(5));\n });\n });\n}\n\n\n**Widget testing:**\n\nvoid main() {\n testWidgets('Counter increments smoke test', (WidgetTester tester) async {\n await tester.pumpWidget(MyApp());\n \n expect(find.text('0'), findsOneWidget);\n expect(find.text('1'), findsNothing);\n \n await tester.tap(find.byIcon(Icons.add));\n await tester.pump();\n \n expect(find.text('0'), findsNothing);\n expect(find.text('1'), findsOneWidget);\n });\n}\n\n\n**Integration testing:**\n\nvoid main() {\n group('App', () {\n testWidgets('full app test', (tester) async {\n app.main();\n await tester.pumpAndSettle();\n \n // Test complete user flow\n await tester.tap(find.byKey(Key('login_button')));\n await tester.pumpAndSettle();\n \n expect(find.text('Welcome'), findsOneWidget);\n });\n });\n}\n\n\n**Mocking:**\n• Use mockito package\n• Mock HTTP requests\n• Mock platform channels