Hypothesis approach looks interesting. I’ll look into it.
As for my approach to generation, there’s not much to it. Instead of generating arbitrarily complex values and then trying to shrink them to simpler ones, I start with simple values and, if they work, proceed to more complex ones. In every test run I use the same values. It’s basically a brute-force, which omits values which are sufficiently similar to values already tested.
The omission is achieved by having a base set of simple values where each is judged by me to be sufficiently different from the others (I basically copy e.g. tricky numbers/unicode values from quickcheck implementations, which are used inside generating code), and the base set is ordered from simplest to less simple. Then I run a loop which goes over all elements of the base set, run the test, then take a function which based on the base set produces more complex values, run the test on that etc. So the earliest fail is going to be the simplest value it can generate.
As for my approach to generation, there’s not much to it. Instead of generating arbitrarily complex values and then trying to shrink them to simpler ones, I start with simple values and, if they work, proceed to more complex ones. In every test run I use the same values. It’s basically a brute-force, which omits values which are sufficiently similar to values already tested.
The omission is achieved by having a base set of simple values where each is judged by me to be sufficiently different from the others (I basically copy e.g. tricky numbers/unicode values from quickcheck implementations, which are used inside generating code), and the base set is ordered from simplest to less simple. Then I run a loop which goes over all elements of the base set, run the test, then take a function which based on the base set produces more complex values, run the test on that etc. So the earliest fail is going to be the simplest value it can generate.