Agent Skills: Testing Skill

Testing Skill

Standards and workflow for writing and running tests. Every feature must be tested.

Announce at start: "I'm using testing skill to ensure proper test coverage."

Trigger Conditions

• Writing new tests for a feature or bug fix
• Adding a new feature (must include tests)
• Modifying logic that has existing tests (must update them)
• Before claiming work is complete
• Before committing code

Framework

Vitest 4 — configured in vitest.config.ts.

Test Structure

tests/
├── unit/          # Individual functions, utilities, components
├── integration/   # IPC, database, service interactions
├── regression/    # Regression test cases
└── e2e/           # End-to-end tests (Playwright, playwright.config.ts)

Two Test Environments

| Environment | When | File naming | | ---------------- | --------------------------------- | --------------- | | node (default) | Main process, utilities, services | *.test.ts | | jsdom | DOM/browser-dependent code | *.dom.test.ts |

Workflow

Step 1: Identify What to Test

Before writing tests, list the riskiest scenarios first:

• What happens when the dependency returns undefined / throws?
• What happens at boundaries (empty list, max retries, past timestamp)?
• What is most likely to break in production?

Step 2: Write Tests

Follow these quality rules:

1. Describe behavior, not code structure

// Wrong — describes implementation
it('should call repo.getConversation', ...)

// Correct — describes behavior
it('should return cached task without hitting repo on second call', ...)
it('should reject with error when conversation does not exist', ...)

2. Every describe block must cover at least one failure path

Happy-path-only tests leave the most dangerous code untested.

3. One behavior per test

Keep each it() focused. More than 3 expect() calls in one test is a signal it is testing too much at once.

4. Self-check

After writing a test, mentally delete the core logic it targets. If the test would still pass, rewrite it — it is not guarding anything.

5. Start from risk, not from coverage gaps

List scenarios most likely to produce bugs. Write those first. Coverage is the outcome, not the starting point.

Step 3: Run Tests

bun run test              # Run all tests (REQUIRED before every commit)
bun run test:coverage     # Check coverage (before opening a PR)

Step 4: Verify Coverage

Coverage target: ≥ 80% for all source files matched by vitest.config.ts → coverage.include (currently src/**/*.{ts,tsx} plus a few scripts).

New source files are automatically included in coverage — no manual config changes needed. If a new file is accidentally excluded by a rule in coverage.exclude, remove it from the exclude list.

Step 5: Update Existing Tests

When modifying logic, check if existing tests need updating:

bun run test -- --reporter=verbose   # See which tests pass/fail with names

If a test fails because the behavior changed intentionally, update the test. If it fails unexpectedly, investigate.

Edge Case Checklist

When testing a module, verify:

• [ ] null / undefined inputs handled
• [ ] Empty arrays/objects handled
• [ ] Error thrown by dependencies handled
• [ ] Boundary values (0, -1, max, empty string)
• [ ] Async operations (timeout, rejection, cancellation)

Quick Checklist

Before submitting code:

• [ ] New features have corresponding test cases
• [ ] Modified logic has updated tests
• [ ] bun run test passes
• [ ] Tests describe behavior, not implementation
• [ ] At least one failure path per describe block
• [ ] New source files are not accidentally excluded by coverage.exclude
• [ ] bun run test:coverage meets ≥ 80% target

Common Mistakes

| Mistake | Correct | | --------------------------------- | --------------------------------------------- | | Testing implementation details | Test observable behavior | | Only testing happy path | Must include at least one failure path | | 5+ expects in one it() | Split into separate tests | | Skipping tests for "simple" code | Simple code breaks too — test the risky parts | | Writing tests after saying "done" | Tests are part of "done", not an afterthought |