Testing Rules
These rules are mandatory for all test-related work.
TDD Workflow
RED → GREEN → REFACTOR (all new code).
Test Strategy
| Layer | Test Type | Mock Strategy |
|---|---|---|
| Functional Core | Unit Test | No mocks needed (pure input→output) |
| Imperative Shell | Integration | Testcontainers (real DB/services) |
| External APIs | Test Double | With // Test Double rationale: [reason] |
Forbidden Patterns
These patterns are never acceptable:
| Pattern | Why Forbidden | Alternative |
|---|---|---|
jest.fn() for Repository/Service/Domain |
Invalid test — doesn't prove production works | Testcontainers |
class InMemoryRepository |
Diverges from real DB behavior | Real DB container |
class MockXxx / class FakeXxx |
Hides integration issues | Direct instantiation or Testcontainers |
jest.mock('../services/X') |
Skips real collaboration | Test real collaboration |
it.skip('...database...') |
"Too slow" is not valid | Testcontainers are fast enough |
Coverage Requirements
- 80% overall minimum
- 100% Functional Core (pure logic must be fully tested)
- Critical paths for Imperative Shell
Dev/Prod Parity
Tests must use real dependencies:
- Real database via Testcontainers (not in-memory substitutes)
- Config via environment variables
- Mock tests passing ≠ production working
Detection Checklist
When analyzing test files, flag:
- Any
jest.fn()usage on Repository, Service, or Domain classes - Any
InMemory*orMock*orFake*class definitions - Any
jest.mock()calls on internal modules - Any skipped tests with database/slow excuses
- Missing error case coverage
- Missing edge case coverage
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