This interesting testing tool was pointed out to me by Ned Batchelder when he was on The Changelog.
It combines human understanding of your problem domain with machine intelligence to improve the quality of your testing process while spending less time writing tests.
At its core, Hypothesis is a modern implementation of property based testing, which came out of the Haskell world 20 (!) years ago.
Hypothesis runs your tests against a much wider range of scenarios than a human tester could, finding edge cases in your code that you would otherwise have missed. It then turns them into simple and easy to understand failures that save you time and money compared to fixing them if they slipped through the cracks and a user had run into them instead.