Wednesday, September 23, 2009

Don't Bother Testing for Null?

This appeared on Rainsberger's blog a couple of days ago
Unless I’m publishing an API for general use, I don’t worry about testing method parameters against null. It’s too much code and too many duplicate tests. Besides, I would be testing the wrong thing.
When a method receives null as a parameter, the invoker—and not the receiver—is missing a test
I think I've got to disagree with him on this one. Unless I'm misunderstanding 'general use'. It might be OK not to test for null if it's just your code calling your code (of course what happens when this gets pushed out, maybe serviceized and suddenly others are calling it?) Even if you do not guarantee the right results if the method is passed a null, I would think you should at least make sure that it doesn't blow up. If it fails, it should fail gracefully. It's true that it's not the responsibility of the receiver to make sure the invoker is calling it correctly, and I wouldn't expect a test for every conceivable possibility necessarily. But nulls happen all the time, its not unreasonable to expect a quick check. There wouldn't even be a lot of code. something like
if (someVar == null) {
    Log.error("it was null");

would do nicely. I do agree there is test duplication between the reciever and invoker, in that both are testing for the null condition on the same variable, but this doesn't really bother me. It seems to me there are lots of tests that have overlap or dependencies. Maybe I'm just crazy. I left a comment on the post.