unexpected

<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=0"> <link rel="stylesheet" href="../../../static/normalize.css" type="text/css" media="screen" /> <link rel="stylesheet" href="../../../static/main.css" type="text/css" media="screen" /> <link rel="shortcut icon" type="image/vnd.microsoft.icon" href="../../../static/bug-icon-black.ico"> <title>function - to call the callback</title> </head> <body class="sidebar-hidden has-sidebar"> <header> <div class="logo-icon"></div> <nav> <ul> <li class="menu-toggle-item"> <button class="menu-toggle" onclick="toggleSidebar()"></button> </li> <li class=""><a href="../../..">Unexpected</a></li> <li class="active"><a href="../../any/to-be">Assertions</a></li> <li class=""><a href="../../../api/addAssertion">API</a></li> <li class=""><a href="../../../plugins">Plugins</a></li> </ul> </nav> <div class="search" style="visibility: hidden"> <input id="search" 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href="../../array-like/to-contain">to contain</a> </li> <li class=""> <a href="../../array-like/to-have-items-satisfying">to have items satisfying</a> </li> <li class=""> <a href="../../array-like/to-have-length">to have length</a> </li> <li class=""> <a href="../../array-like/when-passed-as-parameters-to">when passed as parameters to</a> </li> </ul> </li> <li> <h3>Buffer</h3> <ul> <li class=""> <a href="../../Buffer/when-decoded-as">when decoded as</a> </li> </ul> </li> </ul> </nav> <div class="main" tabindex="-1"> <div class="content"> <h1>to call the callback</h1> <p>Asserts that a node.js-style asynchronous function taking a single callback will call it.</p> <div class="code lang-javascript"> <div><span style="color: #a71d5d">function</span> <span style="color: #000000">mySuccessfulAsyncFunction</span><span style="color: #000000">(</span>cb<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>    <span style="color: #000000">setTimeout</span><span style="color: #000000">(</span><span style="color: #a71d5d">function</span> <span style="color: #000000">()</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #000000">cb</span><span style="color: #000000">();</span></div> <div>    <span style="color: #000000">});</span></div> <div><span style="color: #000000">}</span></div> <div> </div> <div><span style="color: #a71d5d">return</span> <span style="color: #000000">expect</span><span style="color: #000000">(</span>mySuccessfulAsyncFunction<span style="color: #000000">,</span> <span style="color: #df5000">'to call the callback'</span><span style="color: #000000">);</span></div> </div><p>If the callback is never called, it will hang until your test framework marks it as timed out. So the assertion itself only ever fails if the function throws an exception synchronously:</p> <div class="code lang-javascript"> <div><span style="color: #a71d5d">function</span> <span style="color: #000000">errorOut</span><span style="color: #000000">(</span>cb<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>    <span style="color: #a71d5d">throw</span> <span style="color: #a71d5d">new</span> Error<span style="color: #000000">(</span><span style="color: #df5000">'ugh'</span><span style="color: #000000">);</span></div> <div><span style="color: #000000">}</span></div> <div><span style="color: #a71d5d">return</span> <span style="color: #000000">expect</span><span style="color: #000000">(</span>errorOut<span style="color: #000000">,</span> <span style="color: #df5000">'to call the callback'</span><span style="color: #000000">);</span></div> </div><div class="output"> <div><span style="color: red; font-weight: bold">ugh</span></div> </div><p>The assertion will pass even if the function passes an error to the callback. If you want that case to fail, look into the <a href="/assertions/function/to-call-the-callback-without-error/">to call the callback without error</a> assertion.</p> <p>If you want the parameters passed to the callback to be the subject of further assertions, you might be able to use the <a href="/assertions/array-like/when-passed-as-parameters-to/">when passed as parameters to</a> assertion.</p> <p>The parameters passed to the callback are also provided as the value of the returned promise, so you can do further assertions like this:</p> <div class="code lang-javascript"> <div><span style="color: #a71d5d">function</span> <span style="color: #000000">asyncFn</span><span style="color: #000000">(</span>cb<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>    <span style="color: #000000">setTimeout</span><span style="color: #000000">(</span><span style="color: #a71d5d">function</span> <span style="color: #000000">()</span> <span style="color: #000000">{</span></div> <div>        <span style="color: #000000">cb</span><span style="color: #000000">(</span><span style="color: #a71d5d">null</span><span style="color: #000000">,</span> <span style="color: #df5000">'foo'</span><span style="color: #000000">);</span></div> <div>    <span style="color: #000000">});</span></div> <div><span style="color: #000000">}</span></div> </div><div class="code lang-javascript"> <div><span style="color: #a71d5d">return</span> <span style="color: #000000">expect</span><span style="color: #000000">(</span>asyncFn<span style="color: #000000">,</span> <span style="color: #df5000">'to call the callback'</span><span style="color: #000000">).</span><span style="color: #000000">then</span><span style="color: #000000">(</span><span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>args<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>   <span style="color: #969896"> // args will be [null, 'foo'];</span></div> <div><span style="color: #000000">});</span></div> </div><p>Or using the Bluebird-specific <code>.spread</code> extension:</p> <div class="code lang-javascript"> <div><span style="color: #a71d5d">return</span> <span style="color: #000000">expect</span><span style="color: #000000">(</span>asyncFn<span style="color: #000000">,</span> <span style="color: #df5000">'to call the callback'</span><span style="color: #000000">).</span><span style="color: #000000">spread</span><span style="color: #000000">(</span><span style="color: #a71d5d">function</span> <span style="color: #000000">(</span>err<span style="color: #000000">,</span> result<span style="color: #000000">)</span> <span style="color: #000000">{</span></div> <div>   <span style="color: #969896"> // err will be null</span></div> <div>   <span style="color: #969896"> // result will be 'foo'</span></div> <div><span style="color: #000000">});</span></div> </div> </div> </div> </section> <script type="text/javascript"> baseUrl = '../../..'; </script> <script type="text/javascript" src="../../../static/toggleSidebar.js"></script> <script type="text/javascript" src="../../../static/rememberScrollPosition.js"></script> <script type="text/javascript" src="../../../static/focusMain.js"></script> <script type="text/javascript" src="../../../static/search.js"></script> </body> </html>