Unit Testing

unit-testing

Registry Trigger

Use when

• test pure logic edge cases invariants branches and failure paths

Do not use when

• no task-local unit testing decision is required

Skill Role

Prove local observable behavior through deterministic seams, faithful doubles, strong assertions, cleanup, and explicit unit-proof limits. Exclude real-boundary, journey, portfolio, and release decisions.

High-Value Rules

• Separate ordinary behavior proof from regression proof. Recreate changed inputs, states, branches, or dependency responses and assert observable allowed and denied outcomes without inventing a prior failure.
• Consume known-failure evidence conditionally. When an accepted defect, incident, or review finding exists, use regression-testing for causal trigger, counterfactual, fixture, and same-pattern decisions.
• Assert stable observable behavior. Prefer public outcomes and important invariants over private call order or helper structure, and cover denied or absent effects where silent mutation would matter.
• Control relevant nondeterminism. Place owned seams around clock, randomness, identifiers, scheduling, environment, and mutable global state only where they affect the rule under test.
• Match doubles to the risky contract. Preserve required dependency semantics without inferring infrastructure behavior from a convenient fake.
• Challenge consequential assertions proportionately. Invert a guard or perturb a fixture when it materially improves confidence; require red-before-fix, mutation, or fault evidence only under the selected regression contract.
• Own isolation and cleanup. Reset changed state and release fixtures, scheduled work, or temporary resources across success, failure, and cancellation paths.
• State the proof boundary. Unit evidence covers inspected local behavior, not framework wiring, persistence constraints, serialization, network compatibility, provider behavior, production timing, or release readiness.

Anti-Patterns

• Call an ordinary behavior test a regression guard without an accepted prior failure, or claim known-failure coverage without reproducing its mechanism.
• Couple tests to private structure so a behavior-preserving refactor invalidates the evidence.
• Retry or quarantine leaked-state failures, or promote a green unit command to system proof.

Stop Conditions

Escalate when behavior or invariants are unclear, the causal failure cannot be represented locally, a required seam lacks an owner, or the double cannot preserve material boundary semantics. Also escalate when cleanup can contaminate other evidence or the claim depends on a real integration outside unit scope.

Output Contract

• unit behavior proof with changed local behavior or invariant, observable and denied outcomes, deterministic seams, double-fidelity limits, proportionate assertion challenge, cleanup evidence, and explicit proof boundary

Targeted References