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A Dart package that makes testing blocs and cubits easy. Built to work with bloc and mocktail.

Learn more at bloclibrary.dev!

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Create a Mock

import 'package:bloc_test/bloc_test.dart';

class MockCounterBloc extends MockBloc<CounterEvent, int> implements CounterBloc {}
class MockCounterCubit extends MockCubit<int> implements CounterCubit {}

Stub the State Stream

whenListen creates a stub response for the listen method on a bloc or cubit. Use whenListen if you want to return a canned Stream of states. whenListen also handles stubbing the state to stay in sync with the emitted state.

// Create a mock instance
final counterBloc = MockCounterBloc();

// Stub the state stream
whenListen(
  counterBloc,
  Stream.fromIterable([0, 1, 2, 3]),
  initialState: 0,
);

// Assert that the initial state is correct.
expect(counterBloc.state, equals(0));

// Assert that the stubbed stream is emitted.
await expectLater(counterBloc.stream, emitsInOrder(<int>[0, 1, 2, 3]));

// Assert that the current state is in sync with the stubbed stream.
expect(counterBloc.state, equals(3));

Unit Test with blocTest

blocTest creates a new bloc-specific test case with the given description. blocTest will handle asserting that the bloc emits the expected states (in order) after act is executed. blocTest also handles ensuring that no additional states are emitted by closing the bloc stream before evaluating the expectation.

setUp is optional and should be used to set up any dependencies prior to initializing the bloc under test. setUp should be used to set up state necessary for a particular test case. For common set up code, prefer to use setUp from package:test/test.dart.

build should construct and return the bloc under test.

seed is an optional Function that returns a state which will be used to seed the bloc before act is called.

act is an optional callback which will be invoked with the bloc under test and should be used to interact with the bloc.

skip is an optional int which can be used to skip any number of states. skip defaults to 0.

wait is an optional Duration which can be used to wait for async operations within the bloc under test such as debounceTime.

expect is an optional Function that returns a Matcher which the bloc under test is expected to emit after act is executed.

verify is an optional callback which is invoked after expect and can be used for additional verification/assertions. verify is called with the bloc returned by build.

errors is an optional Function that returns a Matcher which the bloc under test is expected to throw after act is executed.

tearDown is optional and can be used to execute any code after the test has run. tearDown should be used to clean up after a particular test case. For common tear down code, prefer to use tearDown from package:test/test.dart.

tags is optional and if it is passed, it declares user-defined tags that are applied to the test. These tags can be used to select or skip the test on the command line, or to do bulk test configuration.

group('CounterBloc', () {
  blocTest(
    'emits [] when nothing is added',
    build: () => CounterBloc(),
    expect: () => [],
  );

  blocTest(
    'emits [1] when CounterIncrementPressed is added',
    build: () => CounterBloc(),
    act: (bloc) => bloc.add(CounterIncrementPressed()),
    expect: () => [1],
  );
});

blocTest can optionally be used with a seeded state.

blocTest(
  'emits [10] when seeded with 9',
  build: () => CounterBloc(),
  seed: () => 9,
  act: (bloc) => bloc.add(CounterIncrementPressed()),
  expect: () => [10],
);

blocTest can also be used to skip any number of emitted states before asserting against the expected states. The default value is 0.

blocTest(
  'emits [2] when CounterIncrementPressed is added twice',
  build: () => CounterBloc(),
  act: (bloc) => bloc..add(CounterIncrementPressed())..add(CounterIncrementPressed()),
  skip: 1,
  expect: () => [2],
);

blocTest can also be used to wait for async operations like debounceTime by providing a Duration to wait.

blocTest(
  'emits [MyState] when MyEvent is added',
  build: () => MyBloc(),
  act: (bloc) => bloc.add(MyEvent()),
  wait: const Duration(milliseconds: 300),
  expect: () => [isA<MyState>()],
);

blocTest can also be used to verify internal bloc functionality.

blocTest(
  'emits [MyState] when MyEvent is added',
  build: () => MyBloc(),
  act: (bloc) => bloc.add(MyEvent()),
  expect: () => [isA<MyState>()],
  verify: (_) {
    verify(() => repository.someMethod(any())).called(1);
  }
);

blocTest can also be used to expect that exceptions have been thrown.

blocTest(
  'throws Exception when null is added',
  build: () => MyBloc(),
  act: (bloc) => bloc.add(null),
  errors: () => [isA<Exception>()]
);

Note: when using blocTest with state classes which don't override == and hashCode you can provide an Iterable of matchers instead of explicit state instances.

blocTest(
  'emits [MyState] when MyEvent is added',
  build: () => MyBloc(),
  act: (bloc) => bloc.add(MyEvent()),
  expect: () => [isA<MyState>()],
);

Dart Versions

• Dart 2: >= 2.12

Maintainers

• Felix Angelov