Laura Inozemtseva

Coverage Is Not Strongly Correlated With Test Suite Effectiveness

Laura Inozemtseva and Reid Holmes

Distinguished paper at ICSE 2014

"In general this paper provides valuable empirical evidence where it was missing." --Reviewer 1

"Overall, I found this paper to be enjoyable to read. It is well written, and the research/results are well justified." --Reviewer 2

"If you manage to address [the reviewers'] points, your paper will become classic reading in the field of test coverage." --PB summary


The coverage of a test suite is often used as a proxy for its ability to detect faults. However, previous studies that investigated the correlation between code coverage and test suite effectiveness have failed to reach a consensus about the nature and strength of the relationship between these test suite characteristics. Moreover, many of the studies were done with small or synthetic programs, making it unclear whether their results generalize to larger programs, and some of the studies did not account for the confounding influence of test suite size.

We have extended these studies by evaluating the relationship between test suite size, coverage, and effectiveness for large Java programs. Our study is the largest to date in the literature: we generated 31,000 test suites for five systems consisting of up to 724,000 lines of source code. We then measured the statement coverage, decision coverage, and modified condition coverage of these suites and used mutation testing to evaluate their fault detection effectiveness.

We found that there is a low to moderate correlation between coverage and effectiveness when the number of tests in the suite is controlled for. In addition, we found that stronger forms of coverage do not provide greater insight into the effectiveness of the suite. Our results suggest that coverage, while useful for identifying under-tested parts of a program, should not be used as a quality target because it is not a good indicator of test suite effectiveness.

Supplementary Material

PDF of the paper


Expanded discussion of related work

Appendix with full data tables


Teaser video (download)

Video of the presentation (download)


    author={Inozemtseva, Laura and Holmes, Reid},
    title={Coverage is Not Strongly Correlated with Test Suite Effectiveness},
    booktitle={Proceedings of the International Conference on Software Engineering},