Harness Engineering Practices P7. Negative Verification — Regression and Blast Radius Gates 🎯 Point Agents optimize for "my change works" and underweight "I haven't broken anything else." Positive verification alone won't catch escaped defects. 📝 Overview Add blast radius checks to completion gates — beyond running the full existing test suite, verify "who imports the symbols I touched." Negative verification confirms not just that your code works, but that nothing else is broken. 🔍 Explanation Agents naturally focus on "tests related to my change pass." But change impact doesn't stop at the changed code. Altering a function signature breaks callers; changing shared module behavior affects all dependents. Negative verification is the explicit mechanism for verifying "nothing was broken." Identify import sites of changed symbols, run their tests too. Embedding impact visualization and test execution into the completion gate structurally prevents escaped defects. 🛠 How to Practice - Integrate tooling into completion gates that auto-identifies import sites of changed symbols via static analysis (import analysis, call graphs) - Automatically add identified dependent tests to the execution set alongside the existing test suite - Visualize change blast radius (impacted file count, module count) alongside the diff and present it to reviewers - Combine coverage data with static analysis to identify and flag under-tested impact areas 💼 Use Cases - Issue-to-PR agents: auto-run all dependent tests when shared utilities are modified - Migration agents: verify the full impact zone of API signature changes - Legacy code modernization: cover change ripple effects with characterization tests ⚠ Pitfalls Exhaustive blast radius checking can spiral into running the entire monorepo test suite, which is impractical. Combining static analysis (import analysis, call graphs) with dynamic analysis (coverage data) is most effective. Also, negative verification existing doesn't mean you can neglect positive verification — both are necessary. #HarnessEngineering# #QualityAssurance#