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111 lines
4.9 KiB
111 lines
4.9 KiB
11 months ago
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<a href="https://blog.juliobiason.me"><h1>Julio Biason .Me 4.3</h1></a>
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<p class="lead">Old school dev living in a 2.0 dev world</p>
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<div class="post">
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<h1 class="post-title">On Unit Tests and Layers, Part II</h1>
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<span class="post-date">
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2017-09-15
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<a href="https://blog.juliobiason.me/tags/unit-tests/">#unit tests</a>
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</span>
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<p>After coming with a discussion about unit tests and layers, I got a
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bunch of other insights, specially from a video of Gary Bernhardt
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about "Fast Test, Slow Test".</p>
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<span id="continue-reading"></span>
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<p>Just after posting about
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<a href="https://blog.juliobiason.me/code/on-unittests-and-layers/">who one could see the layers through unit testing</a>,
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I finally watched a video of Gary
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Bernhardt (of the "DestroyAllSoftware" fame) about "Fast Test, Slow Test".</p>
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<p>Basically, what Gary is going after is saying "write tests for the layer ONLY,
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so all your tests are fast". Ok, I can get behind it, in a way. Because layers
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have their behaviour -- in a "mechanical" sense, since they don't require
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human interaction, but behaviour nonetheless -- so you're testing behaviour.</p>
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<p>But that also rises one question: <em>What are you testing?</em> Are you testing the
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<em>component</em> or the <em>application</em>? What do you deliver, anyway? <em>Components</em> or
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an <em>application</em>? How do you make sure you're delivering an application in the
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proper way?</p>
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<p>Testing layer behaviour also has a bad side effect: If you're application
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doesn't need a certain part of your layer -- say, you wrote a validator in the
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model layer, but the powers to be decided it wasn't required anymore --, how
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do you make sure it will go away? Your tests will still test those validators
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-- after all, you're testing your model layer -- and your coverage will still
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point that that piece of code is needed and you'll end up with a bunch of dead
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code that is kept alive only because the tests require them.</p>
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<p>Also, because Gary points out that the "integration tests" are still required,
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you'll end up with a lot more tests than necessary. Why not focus on the
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behaviour your <em>application</em> should have instead of the behaviour your
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<em>layers</em> have?</p>
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<p>I'm not against layer testing per-se, I'm just against writing tests that do
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not reflect the general expected behaviour of the application and duplicating
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tests because you're testing layer after layer and then testing them all
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together. You should test the <em>value</em> of your application, not its components.</p>
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<p>On a side note, Gary still does the same mistake everyone does, calling the
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"all layers" tests "system tests". That's wrong. Just because you're going
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through different layers it doesn't mean it can't be a unit test. It depends
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only on itself? Does it test behaviour? Congratulations, you have a unit test.</p>
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