Mutation testing is a technique where you intentionally introduce small bugs into your code and then run your test suite to see if the tests catch them. If tests still pass after mutations like flipping == to != or removing a require statement, your tests aren't actually protecting your logic. This is especially critical for smart contracts, where bugs can't be patched post-deployment and a single exploit can drain funds. The post advocates for a mindset shift: passing tests don't mean secure code — tests that fail on mutations do.
Sort: