testing

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()).

2. Structure

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

Rules:

• Use setUp for shared object creation; use tearDown for cleanup (closing streams, controllers).
• Keep each test focused on one behavior.
• Nest group() blocks for sub-features when a class has many methods.

3. Naming

Name test cases using "should" to describe expected behavior:

4. Unit Tests vs Widget Tests

Default to unit tests for business logic. Use widget tests when verifying UI rendering, gesture handling, or widget interaction.

5. Widget Test Patterns

Rules:

• Wrap widgets in MaterialApp (or the app's root widget) to provide MediaQuery, Directionality, etc.
• Use pump() for a single frame or pumpAndSettle() when animations must complete.
• Prefer find.byKey over find.text for widgets that may have localized or dynamic text.

6. Mocking Best Practices

• Use mocktail for mocks (no code generation required).
• Call registerFallbackValue() in setUpAll for custom types passed to any().
• Mock at the repository boundary, not at the HTTP/database layer.

7. Test File Organization

• Mirror the lib/ folder structure under test/.
• One test file per source file.
• Name test files <source_file>_test.dart.