100% Test Coverage is a LIE, Here’s Why...

100% test coverage is largely a misleading goal. Line coverage doesn't guarantee meaningful tests — a real-world banking system had 100% coverage with zero assertions. Chasing coverage metrics pushes teams toward slow, broad end-to-end tests with poor isolation, hurting feedback speed. Coverage is better used as a trend indicator than a target. Tracking coverage only for small-scoped unit tests is recommended. Mutation testing and property-based testing are introduced as complementary approaches to validate test quality beyond raw coverage numbers.