Writing your first test may be the hardest one that you ever write, because it just gets easier and easier to "think in terms of tests" as you continue to write them and rely on them. That being said, you should write your first test RIGHT NOW. Get it done with so you don't have to carry along all that baggage of "not knowing how to write tests."
In Perl 5, these two lines will get you started.
Hey! The above document had some coding errors, which are explained below: