Also, adding the _full_directory_path_ to PERL5LIB means that your program will work even if you don't cd into its directory to run it.
In short, put your test module _some_place (site_perl?), then make sure that's first in PERL5LIB for your login. Even if you eventually install it system wide, just remove the copy from your test directory, and you don't have to remember to change your PERL5LIB back.
If you're going to be doing this sort of thing a lot, then
you might want to add '.' to the front of PER5LIB. Then
you'll always look in the local directory first.