I only test on GNU/Linux running on MIPS. We have a (tiny?) testsuite, and any patches to extend that are most welcome.
Before applying a patch, I just do a cursory reading of it and hope that the submitter has tested it sufficiently. Most portability issues can be gleemed from reading the patch, and if they do crop up when a alpha release is made then we just fix them. In short, I don't spend any time testing anything unless it is covered by `make check'. And I don't think anyone else should spend more time on it unless they want to.
