Generally, I like to run all my tests both in normal mode and taint mode. And the prove command's -T switch is very handy for that. By doing that, I can ensure that my module will work from a taint mode program.

Not only that, but verifying that your tests run the same both in normal mode and taint mode can uncover bugs in perl itself, since taint mode has historically been a source of perl bugs and weird differences in behaviour.

The trouble with -T is that "make test" runs the test in taint mode only. I wish there was some way to tell it to run a test twice: once in normal mode and once in taint mode.

To further ensure that your module works in still broader environments, it would be nice to test that it works fine in "persistent" environments, such as mod_perl (e.g. a module that uses an INIT block will not be mod_perl-safe). I don't know of an easy way to test that a module is "persistent-environment-safe".