"Hello World" is a traditional start for learning a new language. For TDDers, the equivalent is surely to write a test framework.
For clojure I started with:
(spec "A Spec describes expected behaviour")
which (until my computer can read english and clojure) I confirm by manual inspection: The spec does indeed describe its expected behaviour).
So I went straight on to
(spec "A Spec runs its body")
which took me about a day. But I learned some stuff about vim, fireplace, paredit, and clojure macros along the way.
Public domain. Chris F Carroll