Code Coverage measures the percentage of source code lines, branches, or paths exercised by the automated test suite. While not a direct measure of test quality, it highlights untested areas where regressions could go undetected. Teams use coverage trends to ensure that new code is accompanied by tests and that critical paths maintain adequate verification.
Percentage of code exercised by tests. Google targets: 60% / 75% / 90%.
Similar dynamics. Monorepos make coverage measurement easier (unified tooling) but the absolute number of tests is larger. Coverage of shared libraries becomes critical since they affect many consumers.
Relatively stable across scales, but shared library coverage becomes critical at scale since low coverage in core modules affects many consumers.
Higher coverage catches more bugs pre-production.
Coverage enables safe refactoring.
Strong test coverage catches AI security flaws before production. DORA #1 success factor.