Well, if it's simple API testing one's after, the Test::Harness module will do that perfectly well. Better are the Test-Unit suite of modules which do more solid unit testing, but Test::Harness is easier to use, and every CPAN module and its mother uses it, so there's plenty of examples.

If you're trying to approximate real-world situations, repeat after me:

"Nothing compares to real-world data."

Don't try to test what happens in the real world. Beta it and use that data instead. Nothing you do will more closely approximate how your application is used.