Test coverage

Test coverage is the share of your code that runs during your automated tests, a rough measure of how much of your product is being checked when you change something. High coverage means most paths are exercised by tests, so a break is likely to trip a red light before it reaches a customer; low coverage means changes fly blind. For a lean founder moving fast, coverage matters most where the stakes are highest. Chasing a perfect coverage percentage is a trap: 100% coverage can still miss the cases that matter, and tests that merely confirm code ran prove little. What counts is meaningful coverage, tests that assert the right value on the paths customers depend on, money, authentication, core workflows, so a regression there is impossible to ship unnoticed. Treat coverage as a guide to where you are exposed, not a score to maximise, and invest your testing effort where failure would actually hurt.