3 articles in Testing
Every team with a legacy codebase hits the same wall: you cannot add tests without refactoring, and you cannot refactor without tests. Characterisation tests are the specific tool — invented by Michael Feathers, amplified by AI — that breaks the loop.
Most teams treat TDD as a way to verify code works. That misses the point entirely. TDD is a design tool — Red-Green-Refactor shapes architecture before implementation, and the failing test is a specification, not a verification step.
Most test suites look healthy — high coverage, all green. But run mutation testing and you'll discover that 80-90% of tests would still pass even if you deleted the code they claim to test. Here's what decorative tests are, why they're dangerous, and how to fix them.