How can I prevent symbol contamination between Clojure tests?

Question

I use simulation-style tests in to ensure that my entire application works correctly. The core Clojure test library is used for tests, executed via Leiningen. As the -main function runs, it defines symbols for later use within its logic. The problem is that if I accidentally use a symbol created in one -main test but never defined in the current -main test, it still has a value. I would expect to get an error that the symbol is undefined, but it seems my test environment is somehow sharing state between deftest executions. How can I deal with this? Move all my convenience-driven symbol definitions to a let statement?

Answer 1

If you are def-ing global vars inside your function, that's generally considered bad practice and reason enough to use let as you suggest instead.

However, you can capture a snapshot the mappings of your namespace.

(def ns-snapshot (ns-map *ns*))

So that after you intern symbols

(def foo 1)
(def bar 2)

You can determine the additions

(reduce dissoc (ns-map *ns*) (keys ns-snapshot))
;=> {bar #'so.core/bar, foo #'so.core/foo}

And un-map them

(doseq [[k v] (reduce dissoc (ns-map *ns*) (keys ns-snapshot))] (ns-unmap *ns* k))

So that you'll get the desired undefined error again

 foo ;=> CompilerException ... Unable to resolve symbol: foo in this context