By convention, where is data accompanying test typically stored in Leiningen projects?
Some possibilities include:
<project_name>/test/<project_name>/data/, <project_name>/test/<project_name>/, or
<project_name>/test/data/.
Please list sources of information or reasons behind your argument.
In terms of directory structure:
With "src/main-style" directory tree, where your main Clojure source lives under src/main/clojure and your tests under src/test/clojure, I would place test data under src/test/resources.
With "src-style" directory tree, where your main Clojure source lives under src and your tests under test, I would place test data under dev-resources or test-resources.
In either case, I would add the appropriate resources directory to :resources for the :dev and/or :test profiles (except "dev-resources" is actually the default path, so nothing needs to be added if you go with it):
(defproject … …
:profiles {:dev {:resources ["src/test/resources"]
… …}
… …}
… …)