Suggest you not get started with Perl::Unit at all. :) You see, Perl::Unit aka Test::Unit appears to have been abandoned, as indicated here and here and here. Note that, unlike Perlish-mainstream Test:: modules, Test::Unit is not based on Test::Builder.

A common mistake I've seen from folks coming from a non-Perl xUnit background is to use Test::Unit in preference to the Perl-mainstream and much more widely used Test::Builder/TAP/Test::More/Test::Class set of modules ... only to regret that decision later. Have a read of the "Other Modules for xUnit Testing in Perl" section of the Test::Class documentation, which compares Test::Class with other xUnit-style Perl testing modules (including Test::Unit and Test::SimpleUnit).