Intermediate Perl (O'Reilly). It will get you started on modules, and testing.

There are a lot of "ways to do it", but for simple cases, I start with Module::Starter (module-starter command). You can create a module template with that tool (including the test directory, etc.). If you already have some code, you can paste it into the module template. Then start working on tests right away!

I don't see much benefit in working with Test::Simple, since Test::More contains Test::Simple's functionality plus more, without much additional fuss.