Comment by sevensor

I use hypothesis to test that the happy path is really happy. I use it to define the set of expected inputs for a function, and it looks for the nastiest possible sets of inputs. It’s kind of the opposite of how I write ordinary tests, where I pick challenging but representative examples. Often I’m just checking some basic property, like “function f is the inverse of function g” for round tripping data through a different representation. Sometimes it’s just “function f does not divide by zero.”. Hypothesis seems to have a library of corner cases that it checks first. If you don’t say you can’t handle floats above 2^53, it will try 2^53, for instance. (That’s the threshold where doubles stop being able to represent every integer.) Often the result of running hypothesis is not a code change but a more precise description of what inputs are valid.