I use the Text::Shoebox module constantly (it's for reading and writing lexicons storied in "SF" format), and I have been using it for years; but I'm still uncovering odd little bugs in it.
So today I sat down and wrote endless tests for it (well, for Text::Shoebox and for its new OO interface Text::Shoebox::Lexicon and Text::Shoebox::Entry). Result: about six bugs found. I dare say that that's all the bugs that were left. A new dist (1.02) is hitting CPAN now.