Jay Fields is a software developer at DRW Trading. He has a passion for discovering and maturing innovative solutions. His most recent work has been in the Domain Specific Language space where he's delivered applications that empowered subject matter experts to write the business rules of the applications. He is also very interested in maturing software design through software testing. Jay is a DZone MVB and is not an employee of DZone and has posted 116 posts at DZone. You can read more from them at their website. View Full User Profile

Clojure: Expectations Ignore A Variable Number Of Args In An Interaction Test

03.29.2013
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Over the past year I've written the same test a few times. 

(expect (interaction (my-fn anything) :never)
(a-fn-that-shouldnt-call-my-fn))

This test accomplishes what I'm looking for when I write it - verification that my-fn isn't called. However, it doesn't prevent me from future regressions where my-fn is called with 0, 2, or 2+ arguments. After being bitten by this issue a few times I decided to add an argument matching function that will accept any value for the argument at it's index, and any value for all of the arguments at a greater index. This argument matching function is anything&

The following example is similar to what's above, except any call to my-fn will result in a failure

(expect (interaction (my-fn anything&) :never)
(a-fn-that-shouldnt-call-my-fn))

My original intent was to protect against the scenario I described above*; however, what I ended up with is actually flexible enough to allow me to test other situations as well. For example, I've often found myself testing that a log message was written at a certain level, but not being interested in testing the actual message. The logging I'm working with allows a variable number of arguments, so anything& is perfect for verifying that no matter what args are passed in, the tests passes as long as the level is set correctly.

(expect (interaction (log :warn anything&))
(log :warn "order" 1 "at" (time/now)))

The anything& matching function gives me an extra bit of flexibility that can come in handy at times.

*which is similar to verifyZeroInteractions in mockito

Published at DZone with permission of Jay Fields, author and DZone MVB. (source)

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