In Clojure, how to unit test an async Pedestal interceptor? - unit-testing

Question

I have an async Pedestal interceptor I want to test:
(def my-interceptor
(io.pedestal.interceptor/interceptor
{:name :my-interceptor
:enter (fn [context]
(as/go
(do
(Thread/sleep 1000)
(assoc context :answer 42))))}))
I first tried a naïve test:
(deftest my-test
(is (= 42
(:answer (io.pedestal.interceptor.chain/execute {} [my-interceptor])))))
This doesn’t work because chain/execute returns nil when it has async interceptors. I tried another solution adding the test in an interceptor just after the tested one:
(deftest my-test
(io.pedestal.interceptor.chain/execute
{}
[my-interceptor
(io.pedestal.interceptor/interceptor
{:name :test
:enter (fn [context]
(is (= 41 (:answer context))) ; should fail
context)})]))
However this doesn’t work because the test terminates before the test is executed, and thus succeeds… even if the test fails a second after:
Ran 1 test containing 0 assertions.
No failures.
FAIL in (my-test) (somefile_test.clj:49)
expected: (= 41 (:answer context))
actual: (not (= 41 42))
In practice my tests suite (using Kaocha) fails because there’s a deftest with no assertion in it.
Given that chain/execute returns nil and not a chan, I can’t wrap it in a as/<!! to block until it terminates.
At this point I’m stuck. Is there anything I can do to test that kind of interceptors?

Answer 1

How about this approach?
(require '[clojure.test :as test])
(require '[clojure.core.async :as async)
(test/deftest async-test []
(let [c (async/chan)]
(future (println "Running mah interceptors") (async/>!! c :done))
(test/is (= :done (async/<!! c)))
(async/close! c)))
That runs the actual interceptor code in a separate thread. Test code just needs to post something to the c when it is done.