property-based-testing

We are looking for a viable design pattern for building Scalacheck Gen (generators) that can produce both positive and negative test scenarios. This will allow us to run forAll tests to validate functionality (positive cases), and also verify that our case class validation works correctly by failing on all invalid combinations of data. Making a simple, parameterized Gen that does this on a one-off basis is pretty easy. For example: def idGen(valid: Boolean = true): Gen[String] = Gen.oneOf(ID.values.toList).map(s => if (valid) s else Gen.oneOf(simpleRandomCode(4), "").sample.get) With the above

The Story: Currently, I have a function-under-test that expects a list of lists of integers with the following rules: number of sublists (let's call it N ) can be from 1 to 50 number of values inside sublists is the same for all sublists (rectangular form) and should be >= 0 and <= 5 values inside sublists cannot be more than or equal to the total number of sublists. In other words, each value inside a sublist is an integer >= 0 and < N Sample valid inputs: [[0]] [[2, 1], [2, 0], [3, 1], [1, 0]] [[1], [0]] Sample invalid inputs: [[2]] # 2 is more than N=1 (total number of sublists) [[0, 1], [2

I thought it's time to try out FsCheck but it proves tougher than I thought. There's a lot of documentation on Arb , generators and so on, but there doesn't seem to be any guidance in how to apply that knowledge. Or I'm just not getting it. What may make it harder to grasp is that the relation between tests, properties, generators, arbitraries, shrinking and, in my case, randomness (some tests automatically generate random data, others don't) is not clear to me. I don't have a Haskell background so that doesn't help much either. Now for the question: how do I generate random integers? My test