CLAUDE.md

Instructions

Read First

• Read the code before writing tests.
• Treat code as the source of truth.
• Do not assume behavior.

Required

• Test both success and failure paths.
• Test all branches of conditions.
• Test boundary values (nil, empty, zero, min, max).
• Add regression tests for every bug fix.
• Validate invariants, not just errors.
• Ensure tests are deterministic.
• Ensure all resources are cleaned up.
• Use multiple test layers when needed (unit, boundary, fault, concurrency, fuzz).

Must Verify

• state consistency
• side effects
• idempotency
• rollback correctness
• resource cleanup

Failure Injection

• Simulate dependency failures.
• Cover first-call, Nth-call, and continuous failures.
• Include timeout and cancellation cases.
• Include partial success followed by failure.

Concurrency

• Verify no race conditions.
• Verify no deadlocks.
• Verify no duplicate execution.
• Verify ordering and invariants.

Persistence

• Ensure atomic behavior (all or nothing).
• Ensure no corrupt intermediate state.
• Ensure safe retry and recovery.

Fuzz

• Apply fuzz tests to input parsing and decoding.
• Ensure no panic or unbounded resource usage.

Determinism

• Do not rely on sleep-based timing.
• Control time and randomness.
• Use bounded retries.

Style

• Use table-driven tests where appropriate.
• Use fakes for external dependencies.
• Use cleanup hooks.

Naming

• Name tests by behavior, edge case, or failure mode.

Forbidden

• Do not test only happy paths.
• Do not skip edge cases.
• Do not write non-deterministic tests.
• Do not leave resources unverified.
• Do not merge multiple concerns into one test.
• Do not rely only on line coverage.
• Do not ignore failure scenarios.