Evalue (is (= exp act)) only once when failing the equality test

[ikappaki]

Hi,

could you please review patch to have (is (= exp act) evaluate its argument only once when failing. It fixes #712.

Previously, the arguments were evaluated once in the when close, and then once more in the :actual and :expected keys.

I haven't introduced a test case, because this issue manifest itself only when the test fails, which inadvertently will fail the test suite. Thus I was expecting perhaps you could reason about its behavior for the review?
(Though now that I think of it, it might be possible to write a test case for the gen-assert multimethod rather than the is case which will fail the test suite)

Here are the result running the same test in #712 with the fix, it only prints :5 once as expected this time:

basilisp.user=> (require '[basilisp.test :refer [deftest is]])
nil

basilisp.user=> (deftest issue
                    (is (= 8 (println :5))))
#'basilisp.user/issue

basilisp.user=> (issue)
:5
{:failures [{:actual nil :message "Test failure: (= 8 (println :5))" :test-section nil :type :failure :expr (= 8 (println :5)) :expected 8 :test-name "issue" :line 2}]}

Thanks