open source answer to unit test: don't.
let me explain. ;)
in a sense, open source is about lowering the development cost, and unit test is more work to do.
one way to lowering deveopment cost, for open source projects, is to let users help testing. then as developers, we should: 1. help users do testing; 2. make every bit of your program testable by users.
the way to help users do testing for us, is to write attractive docs. e.g. write usage docs in ezines. saving the time to write test cases, use the time to write interesting tutorials. write more tutorials.
the way to export every bit of our program so they're testable by users, is to write libs. structure our programs as a bunch of libs plus a small executable. write more docs about the api. see point 1 above.
so. the open source answer to unit testing is: write more libs, write better docs.
that's the open source way to do it. i'm serious. ;)
unit testing is for corporate lusers. ;)