Do you know any open software projects that had particularly interesting / well written unit tests ?
Writing unit tests often feels odd to me, because it seems either too random, too dense, to sparse, .. It would be great to read some real world examples (rather than books, library example code etc)..
I've found this blog post by Misko Hevery to be very useful, especially since he includes links to his actual source code with very well-written unit tests.
Update: Unfortunately, the links in his post are broken now. However, you can find the current source file with a search at http://code.google.com/p/testability-explorer/source/browse/trunk/testability-explorer/src/test/java/com/google/test/metric/collection/KeyedMultiStackTest.java.
I recently had the problem of detecting overlapping date ranges in Python. I was deeply impressed by the elegance of this solution, and in particular the unit tests that accompanied it. They are short, clear, and exhaustive. Also, drawing the cases in ASCII art in the docstring is a stroke of genius, in my opinion.
The only change I made was to split each assert into a separate test, for improved isolation.