Behavior Preservation Checker

Systematic verification that code refactoring, restructuring, or migration preserves the existing observable behavior of the system. This skill provides techniques for comparing before and after states, verifying test coverage, checking interface contracts, and performing semantic equivalence analysis.

When to Use This Skill

Use this skill for:

• Verifying that a refactoring PR introduces no behavioral changes
• Reviewing Extract Method, Move Class, or Rename refactorings for correctness
• Validating that a library migration preserves API contracts
• Confirming that performance optimizations do not alter output
• Checking that dependency upgrades maintain backward compatibility
• Ensuring that code cleanup (dead code removal, formatting) has no side effects
• Auditing automated refactoring tool output for correctness

Trigger phrases: "behavior preservation", "verify refactoring", "check no behavior change", "before and after", "semantic equivalence", "contract check", "refactoring safety", "does this change behavior", "regression check", "safe refactoring"

What This Skill Does