This is eximunit, a utility for testing Exim4 mailservers using Python unit tests. It's backed by exim's debug mode, so the tests are as realistic as possible without actually sending messages.
To get started, grab a clone, make sure eximunit/src is on your Python search path, then start authoring tests!
Examples are in the examples directory
Bugs should be filed at http://bitbucket.org/davidnorth/eximunit