Add a .pm file for tests

Not sure how this ever worked. CPAN Testers reported a bunch of
FAILs saying "Unable to find main_module in the distribution" in
the tests, because there was no .pm. This adds one.

Test failures looked like: http://www.cpantesters.org/cpan/report/91cde38e-034b-11e3-8540-98a55735fcd0
Released 0.20