Bloc Test Package

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

Learn more at bloclibrary.dev!

Create a Mock

import 'package:bloc_test/bloc_test.dart';

class MockCounterBloc extends MockBloc<int> implements CounterBloc {}
class MockCounterCubit extends MockBloc<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]));

// Assert that the stubbed stream is emitted.
await expectLater(counterBloc, 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 cubit-specific test case with the given description. blocTest will handle asserting that the cubit emits the expected states (in order) after act is executed. blocTest also handles ensuring that no additional states are emitted by closing the cubit stream before evaluating the expectation.

build should be used for all cubit initialization and preparation and must return the cubit under test.

act is an optional callback which will be invoked with the cubit under test and should be used to add events to the cubit.

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

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

expect is an optional Iterable<State> which the cubit 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 cubit returned by build.

errors is an optional Iterable of error matchers which the cubit under test is expected to have thrown after act is executed.

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

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

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

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

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

blocTest(
  'CounterBloc emits [1] when CounterEvent.increment is added',
  build: () => CounterBloc(),
  act: (bloc) => bloc.add(CounterEvent.increment),
  wait: const Duration(milliseconds: 300),
  expect: [1],
);

blocTest can also be used to verify internal bloc functionality.

blocTest(
  'CounterBloc emits [1] when CounterEvent.increment is added',
  build: () => CounterBloc(),
  act: (bloc) => bloc.add(CounterEvent.increment),
  expect: [1],
  verify: (_) {
    verify(repository.someMethod(any)).called(1);
  }
);

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

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

Dart Versions

  • Dart 2: >= 2.7.0

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bloc_test