Test clojure instance in deftest

Question

I want to check if the right instance is used.
But while the repl gives me true, the actual test returns nil. Idk why

(ns my-app.queue)

(def queue (atom clojure.lang.PersistentQueue/EMPTY))

(ns my-app.queue-test
  (:require [my-app.queue :as sut]
            [clojure.test :refer :all]))

(deftest queue-type-test
  (is (instance? clojure.lang.PersistentQueue @sut/queue)))

;repl output
;(instance? clojure.lang.PersistentQueue @sut/queue) ;=> true

The command lein test gives me:
FAIL in (queue-type-test) (queue_test.clj:6) expected: (instance? clojure.lang.PersistentQueue (clojure.core/deref sut/queue)) actual: nil

I know the test itself is not really useful, but I can't figure out why this behaves like this.

Small detail, but the first namespace declaration and import in your code don't align. — Michiel Borkent
– Michiel Borkent, Commented Feb 27, 2018 at 16:01
I have the same result running lein test :only my-app.queue-test — ezzato
– ezzato, Commented Feb 27, 2018 at 16:11
It works great for me. Try running lein clean, verify your namespaces are all OK, and re-run lein test. — Alan Thompson
– Alan Thompson, Commented Feb 27, 2018 at 17:16

Igor Kharin · Accepted Answer · 2018-02-28 12:00:04Z

1

tl;dr: both is and @ are macros. Most obvious fix would be something like:

(deftest queue-type-test
  (let [queue @sut/queue]
    (is (instance? clojure.lang.PersistentQueue queue)))

clojure.test docs don't make it immediately obvious, but is is a pretty tricky macro that looks inside its body. Here's a snippet from the docstring:

user> (is (= 5 (+ 2 2)))

FAIL in  (:1)
expected: (= 5 (+ 2 2))
  actual: (not (= 5 4))
false

Notice actual: (not (= 5 4)). It's clear that it did not evaluate = so that it can show us the result of (+ 2 2). Here are all the special cases for assert-expr multimethod.

answered Feb 28, 2018 at 12:00

Igor Kharin

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