Unit Testing with functions that return random results

Question

I don\'t think that this is specific to a language or framework, but I am using xUnit.net and C#.

I have a function that returns a random date in a certain range. I

Answer 1

In addition to testing that the function returns a date in the desired range, you want to ensure that the result is well-distributed. The test you describe would pass a function that simply returned the date you sent in!

So in addition to calling the function multiple times and testing that the result stays in the desired range, I would also try to assess the distribution, perhaps by putting the results in buckets and checking that the buckets have roughly equal numbers of results after you are done. You may need more than 100 calls to get stable results, but this doesn't sound like an expensive (run-time wise) function, so you can easily run it for a few K iterations.

I've had a problem before with non-uniform "random" functions.. they can be a real pain, it's worth testing for early.