TDD Workflow Skill

Implement features using strict Test-Driven Development methodology.

The Red-Green-Refactor Cycle

1. RED - Write a Failing Test

1. Understand the requirement
2. Write a test that describes the expected behavior
3. Run the test - confirm it FAILS
4. Commit: "test: add failing test for [feature]"

2. GREEN - Make It Pass

1. Write the MINIMUM code to make the test pass
2. No extra features, no "while I'm here" changes
3. Run the test - confirm it PASSES
4. Commit: "feat: implement [feature]"

3. REFACTOR - Improve the Code

1. Clean up the implementation
2. Remove duplication
3. Improve naming
4. Run tests - confirm they still PASS
5. Commit: "refactor: clean up [feature]"

Test Quality Rules

Good Tests

• •Test behavior, not implementation
• •One assertion per test (when practical)
• •Descriptive test names: "should [expected behavior] when [condition]"
• •Independent - no shared state between tests
• •Fast - mock external dependencies

Bad Tests

• •Testing implementation details
• •Multiple unrelated assertions
• •Flaky tests that sometimes fail
• •Tests that require specific order

Test Structure (Arrange-Act-Assert)

describe('calculateTotal', () => {
  it('should apply discount when coupon is valid', () => {
    // Arrange
    const cart = { items: [{ price: 100 }] };
    const coupon = { discount: 0.1 };

    // Act
    const total = calculateTotal(cart, coupon);

    // Assert
    expect(total).toBe(90);
  });
});

When to Mock

DO Mock:

• •External APIs
• •Database calls
• •File system operations
• •Time-dependent functions
• •Third-party services

DON'T Mock:

• •The code you're testing
• •Simple utility functions
• •Internal collaborators (usually)

TDD Commands

Before implementing any feature:

1. •Ask: "What test would prove this works?"
2. •Write that test
3. •Watch it fail
4. •Implement just enough
5. •Watch it pass
6. •Refactor if needed

Integration with CI

Ensure all tests pass before:

• •Committing code
• •Creating PRs
• •Merging to main