As pleasant as it might be to believe otherwise , there's a whole world outside of Perl. Fortunately, Perl works well with other programs and other languages, even to the point at which you can use them almost seamlessly from your Perl code.
Good testers don't shy away from testing external code just because it seems difficult. You can use Perl's nice testing libraries and the tricks you've learned so far even if you have to test code written in other languages or programs you can't modify. Perl's that flexible.
This chapter's labs demonstrate how to test Perl programs that you can't refactor into modules, how to test standalone programs, and how to test code that isn't Perl at all.
