Test Driven Development

Test Driven Development

When to Use Me

Use me when:

• write production code
• add feature
• implement
• TDD
• new function
• create endpoint
• add method
• implement this
• write code for

Do not use me for:

• debug
• investigate
• analyze error
• refactor without changing behavior
• documentation
• configuration
• setup
• explore
• spike
• general programming questions
• installation or troubleshooting
• framework-agnostic code help
• bug investigation (use systematic-debugging first)

Workflow

1. Identify behavior to implement
2. Write failing test (RED) - one behavior, clear name, real code
3. Verify test fails correctly - MANDATORY, never skip
4. Write minimal code to pass (GREEN) - simplest possible
5. Verify all tests pass - MANDATORY, check other tests too
6. Refactor while staying green (REFACTOR) - clean up only
7. Repeat for next behavior

Error Handling

• Code written before test exists: STOP, request deletion, restart with test
• Test passes immediately: Verify test tests the right thing, not existing behavior
• Multiple behaviors in one test: Ask to split into separate tests
• Refactoring with failing tests: STOP, require green tests first
• I'll test after: STOP, TDD requires test first - no exceptions
• Keeping code as reference: STOP, delete means delete

Tools

The following tools are available to enforce TDD:

• check-test-exists - Verify test file exists before writing implementation
• validate-tdd-cycle - Check if TDD cycle was followed via git history
• analyze-git-order - Analyze commit order to verify test-first approach

Use these tools to validate TDD compliance automatically.

Quick Tests

Should trigger:

• Create a new API endpoint
• Add user authentication
• Implement a new endpoint with tests first
• Implement payment processing
• Write a login function

Should not trigger:

• Debug this error
• Investigate why tests fail
• Refactor this function (no behavior change)
• Update the documentation
• Configure the server

Functional:

• Write test before implementing login feature
• Follow TDD for new endpoint

References

• references/workflow-playbook.mdx - RED-GREEN-REFACTOR cycle details
• references/anti-patterns.mdx - Testing anti-patterns to avoid

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST

Write code before the test? Delete it. Start over.

Verification Checklist

Before marking work complete:

• Every new function/method has a test
• Watched each test fail before implementing
• Each test failed for expected reason
• Wrote minimal code to pass each test
• All tests pass
• No errors or warnings in output
• Edge cases covered