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Testing Rules

Test Before Commit

Run the relevant test suite before every commit.
All tests must pass before pushing to a shared branch.
Never merge a PR with failing tests.
If a test is flaky, fix it immediately or quarantine with a tracking issue.

Coverage Requirements

Minimum 80% line coverage on new code.
Minimum 75% branch coverage on new code.
Coverage should not decrease on any PR.
Exclude generated code, type definitions, and config from coverage metrics.

Test Quality

Test behavior, not implementation. Tests should survive refactoring.
Each test case tests exactly one thing. One assertion per logical behavior.
Tests must be independent. No shared mutable state. No execution order dependency.
Use descriptive names: should_reject_expired_token over test_token_3.

Test Organization

Mirror source directory structure in test directories.
Keep test utilities and fixtures in a shared __tests__/helpers or testutils directory.
Mark slow tests (>5s) so they can be excluded from fast feedback loops.

Mocking Rules

Mock at boundaries: HTTP, database, filesystem, clock, randomness.
Never mock the unit under test.
Prefer fakes (in-memory implementations) over mocks for complex interfaces.
Assert on behavior and outputs, not on how many times a mock was called.

CI Integration

No skip or todo tests in the main branch. Fix or remove them.
Run tests in CI on every push and every PR.
Fail the build if coverage drops below thresholds.
Run tests in parallel where possible to keep CI fast.
Set a timeout on test suites to catch infinite loops (10 minutes max).

Anti-Patterns

Do not write tests that pass when the code under test is deleted.
Do not test private methods directly. Test through the public interface.
Do not ignore test failures by increasing timeouts.
Do not copy-paste tests. Parameterize instead.