Distributing unit tests.

In this context, I'm referring to distributing unit tests along with a software package, as opposed to executing unit tests in a distributed fashion (which is an interesting topic in its' own right). Unit testing has proven to be an essential development artifact to ensure all use cases are executed correctly. I wish I could say all open source projects distribute unit tests as a component of the package. This is simply not the case. Several projects do, however, include a testing facility which is usually composed of unit tests.

Why, if the authors of these software packages spend time writing all these unit tests, should they be distributed along with the software? After all, they write these unit tests for their own testing. Sometimes an entire testing team is responsible for this task.

I would say that no matter how big a testing team any given project has, they are never going to cover all possible corner cases. That goes without saying (but I'm saying it anyway). Custom operating environments, even some other piece of installed software, could cause unexpected behavior that is in no way handled correctly be the software in question. At least having unit testing available in these situations can offer some clue.