tdd

What I Do

• Guide you through the RED-GREEN-REFACTOR cycle
• Write failing tests first, then implementation
• Ensure tests are meaningful and not just passing
• Prevent common TDD anti-patterns

When to Use Me

Use this skill when:

• Implementing new features
• Fixing bugs (write a failing test that reproduces the bug first)
• Refactoring existing code (ensure tests exist first)

The TDD Cycle

1. RED - Write a Failing Test

1. Write a test for the NEXT small piece of functionality
2. Run the test - it MUST fail
3. If it passes, either:
   - The functionality already exists, or
   - The test is wrong

The test should:

• Test ONE thing
• Have a descriptive name explaining the behavior
• Follow Arrange-Act-Assert pattern

2. GREEN - Make It Pass

1. Write the MINIMUM code to make the test pass
2. Don't worry about elegance yet
3. Hardcoding is acceptable temporarily
4. Run the test - it MUST pass

Rules:

• Only write code that makes a failing test pass
• Don't add functionality without a test
• Keep changes small

3. REFACTOR - Clean Up

1. Improve code quality while keeping tests green
2. Remove duplication
3. Improve naming
4. Extract methods/functions
5. Run tests after EVERY change

Anti-Patterns to Avoid

Anti-Pattern	Problem	Solution
Writing tests after code	Tests validate implementation, not behavior	Always write test first
Testing implementation details	Brittle tests that break on refactor	Test public behavior only
Large test steps	Hard to identify what broke	Smaller increments
Skipping refactor phase	Technical debt accumulates	Always refactor after green
Testing trivial code	Wasted effort	Focus on logic and edge cases

Test Structure

describe('ComponentName', () => {
  describe('methodName', () => {
    it('should [expected behavior] when [condition]', () => {
      // Arrange - set up test data
      // Act - call the method
      // Assert - verify the result
    });
  });
});

Commit Rhythm

1. RED: Don't commit (test is failing)
2. GREEN: Commit with "test: add test for X"
3. REFACTOR: Commit with "refactor: improve X"