Read and follow Test Failure Mindset, including its Python standards route. It owns the investigation protocol; this skill applies it to each supplied failure. Reuse an existing evidence record instead of restarting completed investigation.
Per-failure application
Read the complete relevant test, fixtures, setup/cleanup, stack trace, and product path. Preserve the failed revision and conditions; reproduce safely when permitted. Trace the product and test observation to their earliest demonstrated contract divergence.
For each candidate explanation, identify a discriminating observation and separate observed facts from unverified inference. Verify which requirement governs the expected behavior. A familiar mathematical, library, or API convention alone does not establish this product's contract.
Classify supported defects separately as product implementation, interface/architecture, test oracle, or harness/CI; several may coexist. For missing authority, report the intent decision. For missing execution, report unvalidated behavior rather than silently choosing a side.
Example: divide(10, 0) returning a sentinel versus raising an exception cannot be adjudicated
from the operation's name. A current approved sentinel contract makes a raising implementation
incorrect; an approved error contract makes a sentinel expectation incorrect. Without that
authority, report the ambiguity and the evidence or decision required.
Output
TEST / REVISION / FAILURE:
CONTRACT / AUTHORITY / INVARIANTS:
EXPECTED / OBSERVED / REPRODUCTION LIMITS:
EVIDENCE CHAIN / FIRST DIVERGENCE:
SUPPORTED CAUSE / UNVERIFIED HYPOTHESES:
CORRECTION CATEGORY / RATIONALE:
PROPOSED CHANGE / PRESERVED BEHAVIOR:
VALIDATION: original fault -> intended failure; corrected behavior -> success
REMAINING UNCERTAINTY / NEXT OBSERVATION OR INTENT DECISION:
Do not manufacture cause from an assertion mismatch. Keep correction proposals distinct from work actually performed. When changing a test, explain the authoritative reason and show its relevant fault sensitivity; a collection or setup error does not establish regression protection. Use Comprehensive Test Review for the broader assessment.