With the success of agile methodologies more and more projects develop large test suites to ensure that the system is behaving as expected. Not only do tests ensure correctness, but they also offer a live documentation for the code. However, as the system evolves, the tests need to evolve as well to keep up with the system, and as the test suite grows larger, the effort invested into maintaining tests is a significant activity. In this context, the quality of tests becomes an important issue, as developers need to assess and understand the tests they have to maintain. In this paper we present TestLint, an approach together with an experimental tool for qualifying tests. We define a set of criteria to determine test quality, and we evaluate our approach on a large sample of unit tests found in open-source projects.