test-like-you-mean-itlisted

# Test Like You Mean It ## The failure mode this fixes Agents write tests the way a student grades their own exam. They built the code, they want the code to work, so they write tests that confirm the happy path and assert whatever the code currently returns. The suite goes green, everyone relaxes — and nothing was actually verified. A test written to pass is worse than no test: it's a green light bolted over a blind corner. The tell: tests that mirror the implementation ("returns X when given Y" where X was copied from the function's output), no test that could conceivably fail, no edge regimes, no invariants. Smoke tests presented as verification. This skill replaces that with an adversarial wave: after the build, you switch sides. You are no longer the author defending the code — you are the reviewer trying to break it. Finding a real defect is the *expected outcome*, not an embarrassment. ## When to Use This Skill - A feature, calculation, model, or migration just landed and the next step would be "looks done" - The only tests that exist were written in the same session as the code they test - The suite passes but you couldn't say *what property of the system* it proves - The domain has ground truth to check against — math identities, conservation laws, a reference implementation, a spec, known real-world values - Someone (including you) is about to say "tests pass" as the reason to ship **Don't use when:** the change is trivial plumbing with no behavior (a rename,