Ensure implementation matches the spec's interface contract. Load this skill when writing implementation code or fixing review findings. Covers contract fidelity, spec-implementation consistency, and avoiding test-implementation collusion.
Spec-Alignment
Contract Fidelity
The spec is the source of truth. Read the interface signatures,
return types, and exception clauses in the spec before writing code.
Match every detail: return type (bool vs None vs raises), default
values, parameter names, and exception types (ValueError vs
TimeoutError vs RuntimeError).
If the spec says "raises X on condition Y", the implementation MUST
raise X — returning a sentinel value (e.g., False) is a spec violation.
Test-Implementation Collusion
Never let the test match the implementation when the implementation
violates the spec. If the spec says "raises TimeoutError" but your
implementation returns False, the test must test for TimeoutError,
not False. Fix the implementation, not the test.
After writing tests, cross-check: does every test assertion match the
spec's contract, not just what the code currently does?
Self-Review Before Submission
Before declaring code complete, re-read the spec's interface section
and verify each method's behavior against the spec line by line.
