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Testing

TDD is not optional. Code without tests is a liability.

Coverage Target: 80%+

Type What When
Unit Individual functions, utilities Every function
Integration API endpoints, DB operations Every endpoint
E2E Critical user flows Every release

Test-Driven Development

Mandatory workflow for every feature and bug fix:

1. Write test        → should FAIL (RED)
2. Run test          → confirm it fails
3. Write minimal code → should PASS (GREEN)
4. Run test          → confirm it passes
5. Refactor          → improve code quality
6. Run all tests     → nothing broke
7. Check coverage    → 80%+

Why this order matters:

  • Writing tests first forces you to think about the interface before the implementation
  • A test that passes before you write code doesn't test anything
  • Refactoring with tests is safe; without tests it's gambling

Test Quality Rules

  • Test behavior, not implementation
  • One assertion per test (or one logical group)
  • Tests must be independent (no shared state between tests)
  • Tests must be deterministic (no flaky tests in CI)
  • Mock external dependencies, not internal logic
  • Name tests like sentences: should return 404 when user not found

When Tests Fail

  1. Read the error message — it usually tells you what's wrong
  2. Check test isolation — is shared state leaking?
  3. Verify mocks are correct — stale mocks cause phantom failures
  4. Fix the implementation, not the test (unless the test is wrong)
  5. If you need to change a test, explain why in the commit message