This skill defines how to correctly use the mockito package for mocking in Dart and Flutter tests.
| Use | \nWhen | \n
|---|---|
| Real object | \nPrefer over mocks when practical. | \n
Fake (extends Fake) | \nLightweight custom implementation; override only the methods you need. Prefer over mocks when you don't need interaction verification. | \n
Mock (extends Mock) | \nOnly when you need to verify interactions (call counts, arguments) or stub dynamic responses. | \n
verify assertions; otherwise prefer real or fake objects.@GenerateMocks([MyClass])\n// or for nice mocks (return simple legal values for missing stubs):\n@GenerateNiceMocks([MockSpec<MyClass>()])\nvoid main() { ... }\ndart run build_runner build\ntest/ for mock generation by default.build.yaml if you need to generate mocks outside of test/.@override methods or implementations to a class extending Mock.final mock = MockCat();\n\n// Return a value\nwhen(mock.sound()).thenReturn('Meow');\n\n// Throw an error\nwhen(mock.sound()).thenThrow(Exception('No sound'));\n\n// Calculate response at call time\nwhen(mock.sound()).thenAnswer((_) => computedValue);\n\n// Return values in sequence\nwhen(mock.sound()).thenReturnInOrder(['Meow', 'Purr']);\n@GenerateMocks → throws; @GenerateNiceMocks → returns a simple legal value.throwOnMissingStub(mock) to throw on any unstubbed call.verify(mock.sound()); // called at least once\nverifyNever(mock.eat(any)); // never called\nverify(mock.sound()).called(2); // called exactly twice\nAsync:
\nawait untilCalled(mock.sound()); // wait for the interaction\n// Flexible stubbing\nwhen(mock.eat(any)).thenReturn(true);\nwhen(mock.eat(argThat(isNotNull))).thenReturn(true);\n\n// Named arguments\nwhen(mock.fetch(any, headers: any)).thenReturn(response);\nnull as an argument adjacent to an argument matcher.any or argThat as values, not as argument names.final captured = verify(mock.eat(captureAny)).captured;\nprint(captured.last); // last captured argument\nUse captureThat for conditional capturing.
reset(mock); // clear all stubs AND interactions\nclearInteractions(mock); // clear only recorded interactions\nTo mock a function type (e.g., a callback), define an abstract class with the required signature and generate mocks for it:
\nabstract class Callback {\n void call(String value);\n}\n\n@GenerateMocks([Callback])\nlogInvocations([mock1, mock2]); // print all collected invocations\n