Test Driven Development

Test-Driven Development

Activation Rule

Triggers:

• "Write the test first", "TDD", "red-green-refactor"
• Before implementing any new class or function
• Plan step says "add test for X"
• systematic-debugging recommends a regression test

Override Directive: Always write a failing test before any production code. No exceptions. See tdd.instructions.md for the org-wide mandate.

Language Router

Pick the sub-skill for your language:

The Universal Cycle

Regardless of language:

RED   → Write the smallest test that fails for the right reason.
        Run: confirm it fails (not compilation error — a logic failure).

GREEN → Write the minimum production code to make the test pass.
        No extra logic. No anticipating future cases.

REFACTOR → Clean up without breaking the test.
           Extract, rename, simplify. Keep the bar green.

Stop writing tests when:

• Every acceptance criterion from the plan has a test
• All error paths that can actually happen are covered
• The next test you'd write is testing the framework, not your code

Test Naming Convention

// Pattern: <methodName>_<condition>_<expectedOutcome>
createItem_withDuplicateName_throwsDuplicateItemException
getById_withUnknownId_returnsEmpty
processItem_whenQueueFull_retrysAfterDelay

This makes failure messages self-explanatory.

What NOT to Test

• Framework behaviour (Spring wiring, ORM mappings) — assume they work
• Private methods directly — test them through the public interface
• Configuration classes — test the behaviour they configure
• Getter/setter-only DTOs — no logic, no test needed

Commit Pattern

1. Red commit:   "test: <test name> (failing)"
2. Green commit: "feat/fix: <what you implemented>"
3. Refactor:     "refactor: <what you cleaned up>" (if non-trivial)

Inter-Skill References

• Java TDD → tdd-java for Spring Boot, JUnit 5, Mockito, TestRestTemplate
• React TDD → tdd-react for Vitest, React Testing Library, MSW
• After tests pass → verification-before-completion
• Regression tests → systematic-debugging recommends which test to add

Source: rdwr-akashs/.copilot-shared — distributed by TomeVault.