spec.alpha

spec is a Clojure library to describe the structure of data and functions. 
Specs can be used to validate data, conform (destructure) data, explain 
invalid data, generate examples that conform to the specs, and automatically 
use generative testing to test functions.

Clojure 1.9 depends on this library and provides it to users of Clojure. 
Thus, the recommended way to use this library is to add a dependency on the 
latest version of Clojure 1.9, rather than including it directly. In some 
cases, this library may release more frequently than Clojure. In those cases, 
you can explictly include the latest version of this library with the 
dependency info below.

For more information:

WWW: https://clojure.org/about/spec