And you should note that if this works, you've started writing your test suite! Go ahead and use Test::More/etc. to write this code; you can then keep checking in the tests as you make more of them to figure out what the code does.

You can simulate the Web stuff by sending URLs to your backend server - even if there's a lot of Javascript in the front end, you can just look at the access log to see what URLs were visited and visit those directly with WWW::Mechanize.

Finally, make sure that the code is checked into a source code control system - whatever one you're comfortable with if it's not already in source control. You want the option to explore the code and back out changes that turn out to be wrong.