Writing ClojureScript unit tests

re-frame.test macros

There are some things you need to pay extra attention to when writing ClojureScript unit tests for re-frame. Firstly, you'd want to wrap the body of a deftest with one of:

• run-test-sync Use this when you wish to dispatch events sequentially, and do not need to wait for a chain of events to finish.
• run-test-async This is so you can use wait-for to block until specific event handlers are run. Make sure you're using dispatch-sync instead of the regular async dispatch.

The two macros above also make sure to revert any effects, coeffects, event handlers, etc. that are registered inside their body, to keep re-frame clean for the next unit test to run.

Redefs and stubs

The (with-redefs <bindings> ...) form is invaluable for stubbing arbitrary functions. Most of the time you'll be using this for imcljs.fetch. Note that this only applies to variables inside the calling scope of with-redefs (ie. it won't apply to an event handler dispatched by an event handler you dispatched; it only applies to the first in the chain).

If you need to stub a variable that isn't in your calling scope, you'll need to resort to set!.

(let [orig-fn fetch/session]
  (set! fetch/session (stub-fetch-fn "anon-token"))
  (swap! stubbed-variables conj #(set! fetch/session orig-fn)))

This should do the trick but could cause problems depending on the asynchronicity of your code. (I'd love to wrap this inside a utility function or macro but haven't been successful due to how set! works in JavaScript.)

Documenting assertions

To improve documentation, put your is assertions (which optionally take a message as their second argument) inside the body of (testing "message" ...) forms. Calls to testing may be nested, and all of the strings will be joined together with spaces in the final report.

Resources

• https://github.com/Day8/re-frame-test
• https://juxt.pro/blog/posts/cljs-apps.html
• https://clojurescript.org/tools/testing
• https://clojure.github.io/clojure/clojure.test-api.html