When I write tests for the code in clojurescript and core.async I feel little pain —
with-redefs doesn’t work correctly with go-blocks. For example I have a function:
(defn get-subtitles
[sources limit]
(go (-> (http/get (get-url sources limit))
<!
:body
format-dates)))
And the test for it:
(deftest ^:async test-get-subtitles
(with-redefs [http/get (constantly fixture)]
(go (is (= (<! (get-subtitles const/all 100)) expected))
(done))))
It didn’t work, it actually tries to make http request. Ok, I can try to put with-redefs
inside go-block:
(deftest ^:async test-get-subtitles
(go (with-redefs [http/get (constantly fixture)]
(is (= (<! (get-subtitles const/all 100)) expected)))
(with-redefs [http/get (constantly blank-result)]
(is (= (<! (get-subtitles const/addicted 100)) [])))
(done)))
The first assertion works, but in the second assertion I have previously redefined http/get
and it’s incorrect and the assertion fails — with-redefs permanently changes var
when applied in the go-block.
So I’ve developed a little macro which works like with-redefs and can be used inside of go-block
and with code without core.async:
(defmacro with-reset
[bindings & body]
(let [names (take-nth 2 bindings)
vals (take-nth 2 (drop 1 bindings))
current-vals (map #(list 'identity %) names)
tempnames (map (comp gensym name) names)
binds (map vector names vals)
resets (reverse (map vector names tempnames))
bind-value (fn [[k v]] (list 'set! k v))]
`(let [~@(interleave tempnames current-vals)]
(try
~@(map bind-value binds)
~@body
(finally
~@(map bind-value resets))))))
And usage:
(deftest ^:async test-get-subtitles
(go (with-reset [http/get (constantly fixture)]
(is (= (<! (get-subtitles const/all 100)) expected)))
(with-reset [http/get (constantly blank-result)]
(is (= (<! (get-subtitles const/addicted 100)) [])))
(done)))
I put this macro in clj-di for avoiding copying it between projects.
Tests for this macro on github.
UPD: example updated.