So does Clojure's test.check. Even though Clojure ain't typed you can define "specs" of your data and then have generators generating random data (it's not the only use of specs: they can also be used as a way to verify inputs to functions). The generators data can be used to, say, quickly create fake database with lots of data or fed into test.check which then does fuzzy testing and then tries hard to reduce failing test cases to minimal cases.