Hmm, well to me not bothering to RTFM, or do some basic research (e.g. ask on PerlMonks - a response would've been forthcoming within minutes) is not really a valid excuse for not doing testing. Putting a test suite in place takes time, and if you don't have the time to find out about Apache::Test, then you're clearly not committed to testing.
And why should mod_perl be more difficult to test than anything else? If your modules are properly factored, they should be decoupled from mod_perl. If they're not, well your issue isn't mod_perl, it's your code base.
There *are* valid reasons for not doing testing (but they're typically outside the realm of programming, e.g. management won't allow it (explicitly, or implicitly by not allowing enough time to complete tasks with tests)). I don't believe the fact that your application is mod_perl can be a valid reason. Whoever wrote that may have *actual* valid reasons, but to me, it makes sense to be aware of those (so you can potentially do something about them) than to blame it on something you most likely can't change, and get away with not bothering to write tests.