Regression Testing

regression-testing

Registry Trigger

Use when

• protect a named prior failure mechanism and materially reachable same-pattern variants from recurrence

Do not use when

• no accepted defect, incident, review finding, or equivalent recurrence mechanism exists

Skill Role

Prove non-recurrence of a known failure mechanism at the narrowest boundary that preserves its trigger and observable result. Exclude wider portfolio and release verdicts.

High-Value Rules

• Require causal-trigger reproduction rather than adjacent correct behavior as the recurrence guard.
• Establish counterfactual value: observe the guard fail for the matching reason on unfixed behavior when safe, or challenge the assertion with a targeted mutation or fault. If neither is admissible, state the proof limit and compensating evidence.
• Choose the narrowest admissible boundary that still contains the failure mechanism. A local test is insufficient when serialization, storage, browser, provider, concurrency, or deployment behavior caused the defect.
• Preserve the triggering fixture or a minimized equivalent whose removed fields are shown irrelevant. Own redaction, schema drift, setup, and cleanup across pass, failure, and cancellation paths.
• Map sibling paths, consumers, variants, and duplicate implementations for the same mechanism.
• Classify a match current-task only when it affects Acceptance or a required Invariant within scope, scope-blocker when required work is outside scope, or adjacent otherwise with rationale, residual risk, and no edit.
• Assert allowed and forbidden outcomes, including absence of unauthorized or duplicate side effects. For concurrency or eventual consistency, define admissible result sets and use bounded observation instead of fixed sleeps.
• Do not use broad retry to certify a flaky guard. Isolate nondeterminism with owned clock, randomness, scheduling, and data seams; quarantine or non-automation needs an owner, release consequence, and revisit trigger.

Anti-Patterns

• Calling a new green-only happy-path test a regression guard without showing it constrains the prior failure.
• Following a fixed test pyramid when the original mechanism lives at a real boundary.
• Shrinking fixtures until the triggering condition disappears, or reusing stale incident/CI evidence after material edits.
• Claiming recurrence is closed before all authorized current-task occurrences are fixed, or repairing every discovered sibling regardless of task relation.

Stop Conditions

• Escalate when safe reproduction is infeasible, the failure requires irreversible or shared-environment effects, or material same-pattern exposure remains without compensating detection and accepted ownership.

Output Contract

• recurrence map with failure mechanism, guard boundary, counterfactual evidence, fixture fidelity, same-pattern coverage, freshness, and residual risk

Targeted References