What is Test Coverage? — UK Software Development Guide
Direct Answer
Test coverage (or code coverage) is a metric that measures what percentage of source code is exercised by automated tests. Types of coverage: line coverage (percentage of lines executed), branch coverage (percentage of code branches — if/else paths — executed), and statement coverage. A project with 80% line coverage has 80% of its code executed during the test suite.
Test-coverage in the UK
Test coverage has UK compliance value but must be interpreted carefully. High test coverage does not mean high quality — 100% line coverage with tests that make no meaningful assertions tells you nothing. For UK regulated software: DTAC Domain 3 (NHS) and FCA operational resilience expect evidence of systematic quality control — coverage metrics, alongside quality indicators like defect density, provide this evidence. ClickMasters targets 80% line coverage minimum for UK regulated software (authentication, payment processing, clinical data handling). Unmaintained test suites with low coverage that still pass are a common UK technical due diligence finding — indicating code was written without tests rather than with meaningful coverage.
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