The problem is, I have no idea how to do that. Basically, I don't want to test for things I know. I want to test for all the possible arbitrary text that users could throw, and see if my module can format it to valid html in the manner that the users expected it to do.
While getting a community of smart users to help you test can be useful, it may be hard to come by, especially when you are dealing with code that does a task very similar to one that several other modules do. As an alternative, you might want to explore the ideas of stochastic/random/specification-based testing. In very simplistic terms, this is (if my limited understanding is correct) a way to do tests with input data that is (pseudo)randomly generated but within a specified set of constraints. You might start by looknig at the Test::LectroTest module. There are a number of resources on this concept out on the net. The URL, http://www.acmqueue.com/modules.php?name=Content&pa=showpage&pid=277, seems to keep coming up near the top in my Googling, so it might be a good place to start.
"If God had meant for us to think for ourselves he would have given us brains. Oh, wait..."