Mocktail Skill

This skill defines how to correctly use the mocktail package for mocking in Dart and Flutter tests.

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1. Mock vs. Fake vs. Real Object

Use	When
Real object	Prefer over mocks when practical.
Fake (extends Fake)	Lightweight custom implementation; override only the methods you need. Prefer over mocks when you don't need interaction verification.
Mock (extends Mock)	Only when you need to verify interactions (call counts, arguments) or stub dynamic responses.

• Never add @override methods or implementations to a class extending Mock.
• Only use mocks if your test has verify assertions; otherwise prefer real or fake objects.

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2. Creating Mocks

class MockMyService extends Mock implements MyService {}
class FakeMyEvent extends Fake implements MyEvent {}

No code generation required, unlike Mockito, Mocktail uses noSuchMethod at runtime.

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3. Registering Fallback Values

Register fallback values before using custom types with argument matchers. Do this in setUpAll or at the top of your test:

setUpAll(() {
  registerFallbackValue(FakeMyEvent());
});

• Required for non-nullable custom types used with any(), captureAny(), or captureThat().
• Register fallback values for any custom type used with argument matchers.

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4. Stubbing

final mock = MockMyService();

// Return a value
when(() => mock.fetchData()).thenReturn('result');

// Throw an error
when(() => mock.fetchData()).thenThrow(Exception('error'));

// Dynamic/async response
when(() => mock.fetchData()).thenAnswer((_) async => 'result');

// Future<void>
when(() => mock.doWork()).thenAnswer((_) async {});

• Always stub async methods (returning Future or Future<void>) with thenAnswer.
• Stub every method you expect to be called, even if it's not the focus of your test.

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5. Named Parameters