A metric that measures the percentage of source code executed by automated tests. It helps identify untested parts of a codebase and assess test suite completeness.
The term emerged in the 1960s-70s with early testing frameworks, combining 'code' (from Latin 'codex' meaning book or system of laws) with 'coverage' (from Old French 'covrir' meaning to cover or protect). The concept paralleled the development of structured programming and the need to systematically verify program correctness.
Code coverage is like a heat map of your house showing which rooms you've actually walked through - 90% coverage means 10% of your code is like a mysterious locked room that might contain anything from treasure to monsters! However, high coverage doesn't guarantee good tests, just like visiting every room doesn't mean you cleaned them properly.
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