What is a limitation of using code coverage as a measurement?

Using code coverage as a measurement has the significant limitation that it does not guarantee functional coverage. This means that while a high percentage of code being executed during tests might suggest that the code is well-tested, it does not provide assurance that all functionalities of the software have been adequately tested.

For instance, code coverage metrics can only tell you what lines of code are executed during testing but cannot confirm whether all user scenarios or business rules are addressed. It is entirely possible to have high code coverage with tests that do not validate the application's behavior or outcomes appropriately, as these tests might not reflect real-world usage or edge cases. Therefore, relying solely on code coverage metrics can create a false sense of security regarding the quality and robustness of the software. This reinforces the idea that additional testing methods, such as unit tests and user acceptance testing, are vital to ensure that the software meets its functional requirements comprehensively.