A pretty common pattern I've seen in both Ruby and Elixir is to begin building up the state you want to work with in a test and then drop into a repl using pry (either adding a breakpoint in the code or in the test). I think this allows you to "Write said experiments in the same place [your] code already is".

Maybe I'm just misunderstanding what people in Clojure are doing. Please feel to point me in the right direction.