Dart Add Unit Test

Dart Testing Suite

Contents

• [Unit Testing](#unit-testing)
• [Mocking Dependencies](#mocking-dependencies)
• [Test Coverage](#test-coverage)
• [Workflow: Testing Execution](#workflow-testing-execution)

Unit Testing

Utilize package:test as the standard testing library for Dart CLI and backend applications.

• Organize test files to mirror the lib directory structure. Append _test.dart to test files.
• Group related tests using the group() function.
• Use setUp() and tearDown() for shared test state.
• Write pure logic inside Domain/BLoC and extract to static pure functions for 100% unit test coverage.
• Use string interpolation for test group names: group('$ClassName', ...)
• Structure each test using the Arrange-Act-Assert (Given-When-Then) convention:
• Arrange: Set up mocks, create instances, prepare input data.
• Act: Call the method under test.
• Assert: Verify the output or side effects.
• Separate setup from verification to keep tests readable and maintainable.

Mocking Dependencies

mocktail vs mockito Decision

| Criteria | mocktail (Recommended) | mockito | |---|---|---| | Code generation | Not needed | Requires build_runner | | Setup speed | Fast (extend Mock) | Slower (annotation + codegen) | | Null safety | Full support | Full support | | API style | when(() => mock.method()) | when(mock.method()) | | Best for | Most projects, fast iteration | Large projects with complex APIs |

Rule: Default to mocktail (no codegen, faster setup). Use mockito only when you need @GenerateNiceMocks for complex APIs with many overloads.

mocktail Setup (Recommended)

import 'package:mocktail/mocktail.dart';

// Create mock — no code generation needed
class MockUserRepository extends Mock implements UserRepository {}

void main() {
  late MockUserRepository mockRepo;

  setUp(() {
    mockRepo = MockUserRepository();
  });

  test('fetches user successfully', () {
    // Arrange
    when(() => mockRepo.getUser('1'))
        .thenAnswer((_) async => const User(id: '1', name: 'Alice'));

    // Act
    final user = await mockRepo.getUser('1');

    // Assert
    expect(user.name, 'Alice');
    verify(() => mockRepo.getUser('1')).called(1);
  });
}

mockito Setup (Code-Gen)

import 'package:mockito/annotations.dart';
import 'package:mockito/mockito.dart';

@GenerateNiceMocks([MockSpec()])
import 'user_test.mocks.dart';  // Generated by: dart run build_runner build

Verification APIs

| API | Purpose | |---|---| | verify(() => mock.method()).called(1) | Assert method was called exactly once | | verifyNever(() => mock.method()) | Assert method was never called | | verifyNoMoreInteractions(mock) | Assert no unchecked interactions remain | | verifyInOrder([...]) | Assert methods were called in specific order | | reset(mock) | Clear all stubs and interactions |

Registering Fallback Values

For methods with custom types as parameters:

setUpAll(() {
  registerFallbackValue(const User(id: '0', name: 'fallback'));
});

Test Coverage

• Target 100% logic coverage for domain models and business logic.
• Run coverage with dart test --coverage=coverage or flutter test --coverage.
• See dart-coverage skill for detailed LCOV/HTML report generation.

Workflow: Testing Execution

Follow this sequential workflow when testing a Dart feature. Copy the checklist to track progress.

Task Progress

• [ ] Step 1: Write Unit Tests. Focus on core business logic. Ensure files end with _test.dart.
• [ ] Step 2: Generate Mocks. Run dart run build_runner build to generate mocks if using Mockito.
• [ ] Step 3: Run Tests. Execute dart test.
• [ ] Step 4: Check Coverage. Run dart test --coverage=coverage and verify coverage targets are met.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: dhruvanbhalara
• Source: dhruvanbhalara/skills
• License: MIT
• Homepage: https://dhruvanbhalara.github.io/skills/

Install and usage instructions live in the source repository linked above.