ReddRadar
Agent skill
tdd-workflow
Test-Driven Development methodology for Node.js/TypeScript projects.
Install this agent skill to your Project
npx add-skill https://github.com/aiskillstore/marketplace/tree/main/skills/doubleslashse/tdd-workflow
SKILL.md
TDD Workflow Skill
Overview
Test-Driven Development methodology for Node.js/TypeScript projects.
The RED-GREEN-REFACTOR Cycle
RED Phase: Design Failing Tests
Write tests BEFORE implementation:
- Identify Behavior: What should the code do?
- Design Test Cases: Cover all scenarios
- Write Tests: Use AAA pattern
- Run Tests: Confirm they FAIL
- Verify Failure: Tests fail for the RIGHT reason
GREEN Phase: Minimal Implementation
Make tests pass with minimal code:
- Focus: One failing test at a time
- Implement: Just enough to pass
- Verify: Run tests, confirm GREEN
- Iterate: Next failing test
- Complete: All tests passing
REFACTOR Phase: Improve Design
Improve code while keeping tests green:
- Review: Identify code smells
- Plan: Choose refactoring
- Apply: Make the change
- Verify: Tests still GREEN
- Repeat: Until quality gates met
AAA Pattern
describe('Calculator', () => {
it('should add two numbers correctly', () => {
// Arrange - Set up test conditions
const calculator = createCalculator();
// Act - Execute the behavior
const result = calculator.add(2, 3);
// Assert - Verify the outcome
expect(result).toBe(5);
});
});
Test Naming Convention
Format: should {expectedBehavior} when {scenario}
Examples:
it('should return empty array when input is empty', ...);
it('should throw ValidationError when email is invalid', ...);
it('should emit event when state changes', ...);
Test Categories
Unit Tests
- Test pure functions and logic
- No I/O, no side effects
- Fast execution
- High isolation
describe('validateEmail', () => {
it('should return true for valid email', () => {
expect(validateEmail('user@example.com')).toBe(true);
});
});
Integration Tests
- Test module boundaries
- Include I/O operations
- Test with real (or fake) dependencies
describe('UserService', () => {
it('should persist user to database', async () => {
const db = createTestDatabase();
const service = createUserService({ db });
await service.createUser({ email: 'test@example.com' });
const user = await db.users.findFirst();
expect(user.email).toBe('test@example.com');
});
});
Contract Tests
- Verify API contracts
- Type safety at boundaries
- Response shape validation
describe('API Contract', () => {
it('should return user with expected shape', async () => {
const response = await api.getUser('1');
expect(response).toMatchObject({
id: expect.any(String),
email: expect.any(String),
createdAt: expect.any(Date),
});
});
});
Test Doubles
Stub
Returns canned data:
const stubApi = {
getUser: () => Promise.resolve({ id: '1', name: 'Test' }),
};
Mock
Verifies interactions:
const mockLogger = {
info: jest.fn(),
error: jest.fn(),
};
// Later: expect(mockLogger.info).toHaveBeenCalledWith('message');
Fake
Working implementation:
const createFakeDatabase = () => {
const store = new Map();
return {
save: (entity) => store.set(entity.id, entity),
findById: (id) => store.get(id),
};
};
Spy
Records calls:
const spy = jest.spyOn(service, 'notify');
await service.process();
expect(spy).toHaveBeenCalledTimes(1);
Test Organization
src/
services/
user-service.ts
user-service.test.ts # Co-located unit tests
api/
handlers.ts
handlers.test.ts
tests/
integration/ # Integration tests
user-flow.test.ts
fixtures/ # Shared test data
users.ts
helpers/ # Test utilities
test-context.ts
Anti-Patterns
Testing Implementation Details
// Bad - testing internal state
expect(service._cache.size).toBe(1);
// Good - testing behavior
expect(service.getCachedValue('key')).toBe('value');
Overly Specific Assertions
// Bad - brittle
expect(result).toEqual({
id: '123',
name: 'Test',
createdAt: new Date('2024-01-01'),
updatedAt: new Date('2024-01-01'),
});
// Good - flexible
expect(result).toMatchObject({
id: expect.any(String),
name: 'Test',
});
Test Interdependence
// Bad - tests depend on order
let user;
it('should create user', () => { user = createUser(); });
it('should update user', () => { updateUser(user); }); // Depends on previous
// Good - independent tests
it('should update user', () => {
const user = createUser();
updateUser(user);
});
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