<objective A suite at 90% line coverage with assertion-free tests catches zero bugs — line coverage proves code ran, not that a regression would be caught. This skill measures the right things (branch coverage, mutation score, critical-path coverage), gates them in CI with a ratchet so coverage can only go up, and surfaces gaps by risk instead of chasing a vanity number. It prevents the classic failure: a green coverage badge over a test suite that never asserts anything meaningful, while the payment module sits at 30%. </objective Quick Route | Situation | Go to | |-----------|-------| | Pic…