The biggest problem are the people who don't know how to write proper unit tests. They write tests that depend on each other (and they work great running with Ant, but then all of sudden fail when I run them from Eclipse, just because they run in different order). They write tests that don't test anything in particular - they just debug the code, check the result, and change it into test, calling it "test1". They widen the scope of classes and methods, just because it will be easier to write unit tests for them. The code of unit tests is terrible, with all the classical programming problems (heavy coupling, methods that are 500 lines long, hard-coded values, code duplication) and is a hell to maintain. For some strange reason people treat unit tests as something inferior to the "real" code, and they don't care about their quality at all. :-(
