PracticalStrategist/FsCheckTutorial.html at master · xqguo/PracticalStrategist · GitHub

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          <h1>Testing code with FsCheck</h1>
<p>Testing code is an important part of writing code. Randomized domain testing is a
good way to test the code throughly and identify issues from a different perspective.
For this, <a href="https://fscheck.github.io/FsCheck/">FsCheck</a> is a very good tool. Read this good introduction for <a href="https://fsharpforfunandprofit.com/posts/property-based-testing/">Property based testing </a>.</p>
<h2>A quick example</h2>
<p>If we want to a test that works for all small int bewteen 1 and 100, we could define a random test domain
that test only the necessary range, as shown in the following code.
The test would often fail as we are testing for a smaller range.</p>
<table class="pre"><tr><td class="lines"><pre class="fssnip"><span class="l"> 1: </span>
<span class="l"> 2: </span>
<span class="l"> 3: </span>
<span class="l"> 4: </span>
<span class="l"> 5: </span>
<span class="l"> 6: </span>
<span class="l"> 7: </span>
<span class="l"> 8: </span>
<span class="l"> 9: </span>
<span class="l">10: </span>
<span class="l">11: </span>
</pre></td>
<td class="snippet"><pre class="fssnip highlighted"><code lang="fsharp"><span class="prep">#I</span> <span class="s">&quot;.paket/load/&quot;</span>
<span class="prep">#load</span> <span class="s">&quot;FsCheck.fsx&quot;</span>
<span class="k">open</span> <span onmouseout="hideTip(event, 'fs1', 1)" onmouseover="showTip(event, 'fs1', 1)" class="i">FsCheck</span>
<span class="c">///int arb filtered with range </span>
<span class="k">type</span> <span onmouseout="hideTip(event, 'fs2', 2)" onmouseover="showTip(event, 'fs2', 2)" class="t">SmallInt</span> <span class="o">=</span>
    <span class="k">static</span> <span class="k">member</span> <span onmouseout="hideTip(event, 'fs3', 3)" onmouseover="showTip(event, 'fs3', 3)" class="f">Int</span>() <span class="o">=</span>
        <span class="i">Arb</span><span class="o">.</span><span class="i">Default</span><span class="o">.</span><span class="i">Int32</span>()
        <span class="o">|&gt;</span> <span class="i">Arb</span><span class="o">.</span><span class="i">filter</span> (<span class="k">fun</span> <span class="i">t</span> <span class="k">-&gt;</span> (<span class="i">t</span> <span class="o">&gt;</span> <span class="n">1</span>) <span class="o">&amp;&amp;</span> (<span class="i">t</span> <span class="o">&lt;=</span> <span class="n">100</span>))

<span class="k">let</span> <span class="i">testsmallint</span> <span onmouseout="hideTip(event, 'fs4', 4)" onmouseover="showTip(event, 'fs4', 4)" class="i">s</span> <span class="o">=</span>
    (<span onmouseout="hideTip(event, 'fs4', 5)" onmouseover="showTip(event, 'fs4', 5)" class="i">s</span> <span class="o">&gt;</span> <span class="n">1</span> <span class="o">&amp;&amp;</span> <span onmouseout="hideTip(event, 'fs4', 6)" onmouseover="showTip(event, 'fs4', 6)" class="i">s</span> <span class="o">&lt;</span> <span class="n">11</span>) <span class="o">|@</span> <span class="s">&quot;Input is between 1 and 11&quot;</span>
</code></pre></td>
</tr>
</table>
<p>The test can be ran using Check.One with arguments to
shows the passed tests inputs as well as failed cases with shrink</p>
<table class="pre"><tr><td class="lines"><pre class="fssnip"><span class="l">1: </span>
</pre></td>
<td class="snippet"><pre class="fssnip highlighted"><code lang="fsharp"><span class="i">Check</span><span class="o">.</span><span class="i">One</span>({ <span class="i">Config</span><span class="o">.</span><span class="i">Verbose</span> <span class="k">with</span> <span class="i">MaxTest</span> <span class="o">=</span> <span class="n">5</span>; <span class="i">Arbitrary</span> <span class="o">=</span> [ <span onmouseout="hideTip(event, 'fs5', 7)" onmouseover="showTip(event, 'fs5', 7)" class="i">typeof</span><span class="o">&lt;</span><span onmouseout="hideTip(event, 'fs2', 8)" onmouseover="showTip(event, 'fs2', 8)" class="i">SmallInt</span><span class="o">&gt;</span> ] }, <span class="i">testsmallint</span>)
</code></pre></td>
</tr>
</table>
<table class="pre"><tr><td><pre><code>0:
12
shrink:
11
Falsifiable, after 1 test (1 shrink) (StdGen (1784431804,296632552)):
Label of failing property: Input is between 1 and 11
Original:
12
Shrunk:
11</code></pre></td></tr></table>
<div class="tip" id="fs1">namespace FsCheck</div>
<div class="tip" id="fs2">type SmallInt =<br />&#160;&#160;static member Int : unit -&gt; &#39;a<br /><br />Full name: FsCheckTutorial.SmallInt<br /><em><br /><br />int arb filtered with range </em></div>
<div class="tip" id="fs3">static member SmallInt.Int : unit -&gt; &#39;a<br /><br />Full name: FsCheckTutorial.SmallInt.Int</div>
<div class="tip" id="fs4">val s : int</div>
<div class="tip" id="fs5">val typeof&lt;&#39;T&gt; : System.Type<br /><br />Full name: Microsoft.FSharp.Core.Operators.typeof</div>


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