079 — Unit Testing {Testing}

Purpose

Establish deterministic, fast-feedback unit test infrastructure using Jest or Vitest with Firebase service mocking. Enforce TDD red-green-refactor cycles and maintain coverage above 80% on all modules. [EXPLICIT]

Physics — 3 Immutable Laws

1. Law of Isolation: Every unit test runs in complete isolation — no network, no Firestore, no real Auth. All Firebase services are mocked or emulated. [EXPLICIT]
2. Law of Speed: The full unit suite executes in under 60 seconds. Any test exceeding 5s is a smell — refactor the dependency. [EXPLICIT]
3. Law of Determinism: Same input always produces same output. No date-dependent, random, or order-dependent tests. Flaky = deleted. [EXPLICIT]

Protocol

Phase 1 — Setup

1. Select runner: Vitest (Vite projects) or Jest (legacy/CRA). [EXPLICIT]
2. Configure vitest.config.ts or jest.config.ts with @testing-library/* and Firebase mock paths. [EXPLICIT]
3. Create __mocks__/firebase/ with stubs for auth, firestore, functions, storage. [EXPLICIT]
4. Set coverage thresholds in config: { branches: 80, functions: 80, lines: 80, statements: 80 }. [EXPLICIT]

Phase 2 — TDD Execution

1. Write failing test (RED) — assert expected behavior before implementation. [EXPLICIT]
2. Write minimal code to pass (GREEN) — no gold-plating. [EXPLICIT]
3. Refactor — extract, rename, simplify while tests stay green. [EXPLICIT]
4. Run vitest --coverage or jest --coverage after each cycle. [EXPLICIT]

Phase 3 — CI Gate

1. Add test command to package.json: "test:unit": "vitest run --coverage". [EXPLICIT]
2. Fail CI if coverage drops below thresholds. [EXPLICIT]
3. Generate coverage report artifact (lcov + HTML). [EXPLICIT]

I/O

Input	Output
Source module (.ts/.tsx)	*.test.ts file with 3+ test cases per function
Firebase service dependency	Mock file in __mocks__/firebase/
Coverage config	coverage/ report (lcov, HTML)
CI pipeline trigger	Pass/fail with coverage delta

Quality Gates — 5 Checks

1. Coverage >= 80% on lines, branches, functions, statements. [EXPLICIT]
2. Zero flaky tests — run suite 3x in CI, all must pass. [EXPLICIT]
3. No any in test files — TypeScript strict mode applies to tests. [EXPLICIT]
4. Each test has exactly one assertion concept — no multi-concern tests. [EXPLICIT]
5. Mock accuracy — mocks mirror real Firebase SDK signatures (type-checked). [EXPLICIT]

Edge Cases

• Firestore Timestamps: Mock Timestamp.now() with fixed value via vi.useFakeTimers().
• Auth state changes: Use onAuthStateChanged mock that emits controlled sequences.
• Cloud Functions callable: Mock httpsCallable return with typed response objects.
• Environment variables: Use vi.stubEnv() — never read real .env in tests.

Self-Correction Triggers

• Coverage drops below 80% → block merge, notify author.
• Test execution time exceeds 60s → profile and split slow suites.
• Snapshot tests exceed 20% of suite → convert to explicit assertions.
• Mock drift detected (SDK update) → regenerate mocks from SDK types.

Usage

Example invocations:

• "/unit-testing" — Run the full unit testing workflow
• "unit testing on this project" — Apply to current context

Assumptions & Limits

• Assumes access to project artifacts (code, docs, configs) [EXPLICIT]
• Requires English-language output unless otherwise specified [EXPLICIT]
• Does not replace domain expert judgment for final decisions [EXPLICIT]