When in doubt, I'd just use the built in clojure.test. You can always move to something else later.

Kaocha is a nice runner once you have many, many tests; the output is much more compact than the default runner. And more nicely colorized, I think.

… I realize that what I said means that Kaocha probably isn’t especially interesting for you right now 😅 I’d also just go for the simplest possible solution to begin with, so clojure.test. I’ve had success with doo as a runner, as well, but why bother if you don’t need it.