Towards a deeper understanding of test coverage

Test coverage is traditionally considered as how much of the code is covered by the test suite in whole. However, test suites typically contain different types of tests with different roles, such as unit tests, integration tests and functional tests. As traditional measures of test coverage make no distinction between the different types of tests, the overall view of test coverage is limited to what is covered by the tests in general. This paper proposes a quantitative way to measure the test coverage of the different parts of the software at different testing levels. It is also shown how this information can be used in software maintenance and development to further evolve the test suite and the system under test. The technique is applied to an open‐source project to show its application in practice.