Interesting Test System for Clojure: test.check
A really nice co-worker of mine has been doing some interesting work with random number generators for the test.check clojure library, and I decided this morning to have a look and see what it's all about. After all, I can't imagine something a lot better than the standard clojure.test as it's got everything I've ever needed. But Bret has used it, and Gary has to have started using it for a reason, so I wanted to find out what that was.
I'm very glad I did.
The problem that I've run into with simple unit test frameworks is that they allow you to test specific inputs and outputs. If you want something to run 100 times with random inputs, you could do it, but it wasn't easy. Certainly, the question as to Why? would arise unless you had a testing framework that thought not in terms of specific inputs and outputs - but in the structure of the data.
If we wanted to test a sorting function, then we could check to see if the act of operating on a sorted sequence was the same as the input sequence, then we'd need to be able to make arbitrary sequences, and then verify the structure of the data as well. This is then more like generators and properties - which is what test.check calls them.
In this regard, it's easy to see how you'd use this to test the limits of a function without worrying about making sure you got all the edge conditions in the unit tests. It's the shotgun approach, and in some cases, it can really make short work of finding the edge cases if it's not immediately easy to see them from the code.
There's even a simple macro to allow these tests to run alongside the clojure.test unit tests - which is exactly how I can see using it. There are some things that the unit testing system really works well for, and there are others that a shotgun approach would really help for as well. So a hybrid approach seems to be the best move.
Certainly interesting, and I'll put it into a project soon.