Testing Skill

Write effective, meaningful Flutter and Dart tests that catch real regressions.

When to Use

Use this skill when:

• Writing unit tests for business logic, repositories, or utility classes.
• Writing widget tests for UI components.
• Reviewing existing tests for correctness and coverage.
• Fixing flaky or false-positive tests.
• Deciding between unit tests, widget tests, and integration tests.

---

1. Test Validity

Before writing or accepting a test, ask:

"Can this test actually fail if the real code is broken?"

• Avoid tests that only confirm mocked/fake behavior without exercising real logic.
• Avoid tests that confirm behavior guaranteed by the language or standard library.
• Every test must be capable of catching a real regression.

// BAD, tests the mock, not real logic
test('should return user', () {
  when(() => repo.getUser()).thenReturn(fakeUser);
  expect(repo.getUser(), fakeUser); // Only proves the mock works
});

// GOOD, tests the cubit's state transitions driven by the mock
blocTest<UserCubit, UserState>(
  'should emit loaded state when getUser succeeds',
  build: () {
    when(() => repo.getUser()).thenAnswer((_) async => fakeUser);
    return UserCubit(repo);
  },
  act: (cubit) => cubit.fetchUser(),
  expect: () => [
    const UserState(status: UserStatus.loading),
    UserState(status: UserStatus.loaded, user: fakeUser),
  ],
);

---

2. Structure

Always use group() in test files. Name the group after the class under test:

group('Counter', () {
  late Counter counter;

  setUp(() {
    counter = Counter();
  });

  test('value should start at 0', () {
    expect(counter.value, 0);
  });

  test('should increment value by 1', () {
    counter.increment();
    expect(counter.value, 1);
  });
});