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Author: ploeh

_posts/2022-06-27-test-double-clocks.html

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 		<div class="comment-date">2024-05-08 11:13 UTC</div>
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+	<div class="comment" id="eddb383b90f8416aaecbee862b808df9">
+		<div class="comment-author"><a href="/">Mark Seemann</a> <a href="#eddb383b90f8416aaecbee862b808df9">#</a></div>
+		<div class="comment-content">
+			<p>
+				Thank you for writing. It's a good point that the two alternatives that I compare really only represent different perspectives. As one part becomes more explicit, the other becomes more implicit, and vice versa. I hadn't though of that, so thank you for pointing that out.
+			</p>
+			<p>
+				Perhaps, as you suggest, a better API might be in order. I'm sure this isn't my last round around that block. I don't, however, want to add <code>Now</code>, <code>FutureDate</code>, etc. to the <code>Some</code> API. This module contains a collection of <a href="https://en.wikipedia.org/wiki/Equivalence_class">representative values of various equivalence classes</a>, and in order to ensure test repeatability, <a href="/2017/09/11/test-data-without-builders">they should be immutable</a> and deterministic. This rules out hiding a call to <code>DateTime.Now</code> behind such an API.
+			</p>
+			<p>
+				That doesn't, however, rule out other types of APIs. If you move to <a href="/2017/09/18/the-test-data-generator-functor">test data generators</a> instead, it might make sense to define a 'future date' generator.
+			</p>
+			<p>
+				All that said, I agree that the best way to test time-sensitive code is to model it in such a way that it's deterministic. I've <a href="/2020/02/24/discerning-and-maintaining-purity">touched on this topic before</a>, and most of the tests in the sample code base that accompanies <a href="/ctfiyh">Code That Fits in Your Head</a> takes that approach.
+			</p>
+			<p>
+				The test discussed in this article, however, sits <a href="/2023/07/31/test-driving-the-pyramids-top">higher in the Test Pyramid</a>, and for such <a href="/2012/06/27/FacadeTest">Facade Tests</a>, I'd like to exercise them in as realistic a context as possible. That's why I run them on the real system clock.
+			</p>
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+		<div class="comment-date">2024-05-18 8:45 UTC</div>
+	</div>
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