Test Now, Test Forever: A Philosophy of Perl Programming
"A crash is when your competitor's program dies. When your program dies, it is an 'idiosyncrasy'. Frequently, crashes are followed with a message like 'ID 02'. 'ID' is an abbreviation for idiosyncrasy and the number that follows indicates how many more months of testing the product should have had."
This chapter might appear at first blush to be out of sequence. We're steadily getting more specific in the details of taking over code, and here near the beginning is a chapter on how to do testing. Shouldn't it be near the end?
In a word, no. I am going to describe a philosophy of testing that will revolutionize your development practices if you have not already encountered it. I will show you how to implement it for Perl code and give a detailed example. It is so pivotal to the development process that I want to make sure you see it as soon as possible. So yes, it really should come before everything else.
3.1 Testing Your Patience
Here's the hard part. Creating tests while you're writing the code for the first time is far, far easier than adding them later on. I know it looks like it should be exactly the same amount of work, but the issue is motivation. When robots are invented that can create code, they won't have this problem, and the rest of us can mull over this injustice while we're collecting unemployment pay (except for the guy who invented the robot, who'll be sipping margaritas on a beach somewhere, counting his royalties and hoping that none of the other programmers recognize him).
But we humans don't like creating tests because it's not in our nature; we became programmers to exercise our creativity, but "testing" conjures up images of slack-jawed drones looking for defects in bolts passing by them on a conveyor belt.
The good news is that the Test:: modules make it easy enough to overcome this natural aversion to writing tests at the time you're developing code. The point at which you've just finished a new function is when your antitesting hormones are at their lowest ebb because you want to know whether or not it works. Instead of running a test that gets thrown away, or just staring at the code long enough to convince yourself that it must work, you can instead write a real test for it, because it may not require much more effort than typing:
is(some_func("some", "inputs"), qr/some outputs/, "some_func works");
The bad news is that retrofitting tests onto an already complete application requires much more discipline. And if anything could be worse than that, it would be retrofitting tests onto an already complete application that you didn't write.
There's no magic bullet that'll make this problem disappear. The only course of action that'll take more time in the long run than writing tests for your inherited code is not writing them. If you've already discovered the benefits of creating automated tests while writing an application from scratch then at least you're aware of how much they can benefit you. I'll explore one way to make the test writing more palatable in the next chapter.