Testing your code
It is very important to write tests for the code that you write, to help you quickly understand if any changes you make to your code will break something.
Writing tests can also help you design higher quality code as well as help you test your assumptions of how well you understand the requirements of the application.
Writing testis is also fun and a great way to feel confident about working with other people's code (or code you wrote more than a few days ago)
Writing Tests in Clojure
You write your tests in the same way you write other Clojure code.
Clojure.test is the most common library used to write tests in Clojure and as its part of Clojure itself its easy to get started.