What 100% Test Coverage Can't Measure

What 100% Test Coverage Can't Measure Customers started asking us: "How do you evaluate test quality? What does your evaluation look like?" We had coverage numbers - line, branch, function - and we were driving files to 100%. But we didn't have a good answer for what happens after 100%. Coverage proves every line was exercised. It doesn't say whether the tests are actually good. Coverage Is the Foundation Coverage tells you which lines ran during testing. That's important. A file at 30% coverage