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d="M747.1,121.1V79.3c0-15.8-9.4-22.4-26.6-22.4c-15,0-26.8,6.6-26.8,19.3c0,2.4,0.2,3.3,0.8,5h16.6 c-0.5-2-0.7-5-0.7-7.5c0-9.6,3.6-12.4,9.4-12.4c6.4,0,9.7,2,9.7,14.4v11.2l-20.8,7.7c-10.6,4.1-19.3,8.8-19.3,20.7 c0,10.9,7.5,17.8,18.6,17.8c9.9,0,17.4-6.2,21.9-12.1v-0.1h0.1l0,11.1l26,0.1v-4.5C749.3,127.1,747.1,126.2,747.1,121.1z M729.6,117.8c-4.4,3.3-7.6,5.3-12.1,5.4c-7.7,0-11.2-5.2-11.2-12.6c0-7.7,3.6-11.2,9.8-13.5l13.4-5.4L729.6,117.8L729.6,117.8z"
></path>
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d="M0,0v90.4c0,65.7,50.9,88.5,88.1,105.2h0.1l3,1.4c0.7-0.4,1.4-0.7,2.2-1c0.4-0.2,0.9-0.4,1.3-0.6 c37.3-16.6,88.4-39.5,88.4-105V0H0z M116,132l-2-5.3l-26.6-70c-1.6,4.1-5.3,14-9.3,24.6l-15.3,41.3c-0.7,2-0.3,3,0.2,3.7 c1.1,1.3,3.5,1.3,7.3,1.3H71l0,4.4H42.4l0-4.4h2.2c3.9,0,7.1-1.7,9.5-6.5l2.9-6.6l26.5-67.8l-4.7-12.5h24.7l34.1,89.7l3.1,8.1H116z"
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<h4 class="bd-toc-link">Web Applications II</h4>
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1. Advanced React
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<a href="/web3/module/recnDKrWb24lgaziC/">
Class Components
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The React Lifecycle
</a>
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<li>
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Composing and Sharing Non-Visual Behavior
</a>
</li>
<li>
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Testing Web Applications
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2. Advanced State Management
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<li>
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The Reducer Pattern
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<a href="/web3/module/recSoiWNJzGURrXYh/"> Async Redux </a>
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Testing React
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Client-Side Authentication
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HTTP / AJAX II
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Deploying Web Apps
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<div class="sprint-nav">
<ul class="section-nav">
<li class="toc-entry toc-h2"><a href="#prepare">Prepare</a></li>
<li class="toc-entry toc-h2"><a href="#learn">Learn</a></li>
<li class="toc-entry toc-h2"><a href="#project">Project</a></li>
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<h1 class="bd-title" id="content">Testing React</h1>
<span class="lead">
<p class="bd-lead"></p>
<p>
In this module we introduce common techniques used for
testing React components.
</p>
</span>
<strong
>At the end of this module, you should be able to:</strong
>
<ul>
<li>test React components as the props change</li>
<li>use mocks in web application tests</li>
<li>
test asynchronous API calls that are made in a component
</li>
</ul>
</div>
<div class="alert alert-warning" role="alert">
<h4>Pro Tip</h4>
<p>Know your audience.</p>
</div>
<h2 class="display-4">
<a
id="prepare"
class="anchor"
href="#prepare"
aria-hidden="true"
><span class="octicon octicon-link"></span></a
>Prepare
</h2>
<p class="lead">Review each preclass resource before class.</p>
<div class="preclass">
<ul class="list-group list-group-flush">
<li class="list-group-item">
<a
target="_blank"
href="https://jestjs.io/docs/en/asynchronous"
>Jest Documentation on Testing Asynchronous Code</a
>
</li>
</ul>
</div>
<h2 class="display-4">
<a id="learn" class="anchor" href="#learn" aria-hidden="true"
><span class="octicon octicon-link"></span></a
>Learn
</h2>
<h4 class="mark mb-3 p-2">
Learn to test React components as the props change
</h4>
<h5>Overview</h5>
<p>
Today we’re going to continue working with React Testing
Library to test rendered DOM elements. In this objective, we
will focus on testing data being passed as props, and testing
props changes that may happen in a component.
</p>
<p>
In some cases, when props are updated, you’ll want to run a
secondary test on the same component. With our previous
knowledge of react testing library, this would have been
fairly difficult, but thankfully there is a built in method
called <code class="highlighter-rouge">rerender()</code> that
allows us to pretty easily look at a component with new props.
</p>
<p>
In order to do this we need to add the
<code class="highlighter-rouge">rerender</code> function when
setting up our test for use in testing the component
<strong>after</strong> the prop has been updated.
</p>
<p>
Let’s look at an example where we have some component called
<code class="highlighter-rouge">PhoneNumber</code> that the
user will update with their phone number. We want to show an
error message when the component is empty but pass the test
after the user puts in a number between 0 and 10.
</p>
<div class="language-jsx highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="c1">// name test</span>
<span class="nx">test</span><span class="p">(</span><span class="dl">"</span><span class="s2">entering an invalid value shows an error message</span><span class="dl">"</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="c1">// pull in testing properties - add rerender and debug</span>
<span class="kd">const</span> <span class="p">{</span> <span class="nx">getByLabelText</span><span class="p">,</span> <span class="nx">getByRole</span><span class="p">,</span> <span class="nx">rerender</span> <span class="p">}</span> <span class="o">=</span> <span class="nx">render</span><span class="p">(</span>
<span class="p"><</span><span class="nc">PhoneNumber</span> <span class="p">/></span>
<span class="p">);</span>
<span class="kd">const</span> <span class="nx">input</span> <span class="o">=</span> <span class="nx">getByLabelText</span><span class="p">(</span><span class="sr">/favorite number/i</span><span class="p">);</span>
<span class="c1">// update prop</span>
<span class="nx">fireEvent</span><span class="p">.</span><span class="nx">change</span><span class="p">(</span><span class="nx">input</span><span class="p">,</span> <span class="p">{</span> <span class="na">target</span><span class="p">:</span> <span class="p">{</span> <span class="na">value</span><span class="p">:</span> <span class="dl">"</span><span class="s2">2025550113</span><span class="dl">"</span> <span class="p">}</span> <span class="p">});</span>
<span class="c1">// test component</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">getByRole</span><span class="p">(</span><span class="dl">"</span><span class="s2">alert</span><span class="dl">"</span><span class="p">)).</span><span class="nx">toHaveTextContent</span><span class="p">(</span><span class="sr">/the number is invalid/i</span><span class="p">);</span>
<span class="c1">// test prop updates</span>
<span class="nx">rerender</span><span class="p">(<</span><span class="nc">PhoneNumber</span> <span class="na">phoneNumber=</span><span class="si">{</span><span class="dl">"</span><span class="s2">2025550113</span><span class="dl">"</span><span class="si">}</span> <span class="p">/>);</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<p>
How does this work in practice? In the example above we are
interested in a component called
<code class="highlighter-rouge">PhoneNumber</code>. Since the
first test is testing the component before the prop updates,
the test will fail and show an error message. Once the user
inputs their number however, the second test (the rendering)
should pass. If you were to run this code in your console
that’s exactly what you’d see.
</p>
<h3 id="assert-content-is-not-rendered">
Assert Content is not Rendered
</h3>
<p>
In some cases, we want to make sure that content is
<em>not</em> rendering on the DOM. For example, if a component
should show up on click or, really any time after pageload.
React testing library isn’t exactly built for this as all
<code class="highlighter-rouge">getBy</code> assertions return
an error if they can’t find the thing they’re searching for
(if a return is <code class="highlighter-rouge">null</code>).
Luckily there is a workaround here - the assertion called
<code class="highlighter-rouge">queryByRoll</code> (or any
<code class="highlighter-rouge">queryBy</code> assertion),
will return
<code class="highlighter-rouge">null</code> instead of an
error. This let’s us query for something this
<em>isn’t</em> supposed to be on the DOM. It also allows us to
use an assertion like
<code class="highlighter-rouge">.toBeNull()</code> or
<code class="highlighter-rouge">toBeFalsy()</code>, and then
tests will start passing even when no content is rendered.
</p>
<div class="language-jsx highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="nx">test</span><span class="p">(</span><span class="dl">"</span><span class="s2">entering an invalid value shows an error message</span><span class="dl">"</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="c1">// pull in testing properties - add rerender</span>
<span class="c1">// render the component without a prop</span>
<span class="kd">const</span> <span class="p">{</span> <span class="nx">getByLabelText</span><span class="p">,</span> <span class="nx">getByRole</span><span class="p">,</span> <span class="nx">queryByRole</span><span class="p">,</span> <span class="nx">rerender</span> <span class="p">}</span> <span class="o">=</span> <span class="nx">render</span><span class="p">(</span>
<span class="p"><</span><span class="nc">PhoneNumber</span> <span class="p">/></span>
<span class="p">);</span>
<span class="kd">const</span> <span class="nx">input</span> <span class="o">=</span> <span class="nx">getByLabelText</span><span class="p">(</span><span class="sr">/favorite number/i</span><span class="p">);</span>
<span class="c1">// test component</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">getByRole</span><span class="p">(</span><span class="dl">"</span><span class="s2">alert</span><span class="dl">"</span><span class="p">)).</span><span class="nx">toHaveTextContent</span><span class="p">(</span><span class="sr">/the number is invalid/i</span><span class="p">);</span>
<span class="c1">// test prop updates by rerendering component with different props</span>
<span class="nx">rerender</span><span class="p">(<</span><span class="nc">PhoneNumber</span> <span class="na">phoneNumber=</span><span class="si">{</span><span class="dl">"</span><span class="s2">2025550113</span><span class="dl">"</span><span class="si">}</span> <span class="p">/>);</span>
<span class="c1">// assert that the error message is NOT being rendered (optional)</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">queryByRoll</span><span class="p">(</span><span class="dl">"</span><span class="s2">alert</span><span class="dl">"</span><span class="p">)).</span><span class="nx">toBeNull</span><span class="p">();</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<h5>Follow Along</h5>
<p>
In this section we will continue building tests for dog images
app from the previous objective. In this example there is a
parent component that is in charge of fetching the data from
dog.ceo, and a child component that receives that data as a
prop and displays the dog images on the page. For this
example, we will render the dog images into a new component
after the initial rendering of the page. We need to test if
the dog images appear on rerender.
</p>
<p>
This means we want to test the child component. We will test
that it renders a “getting data” message when it is passed an
empty array as a prop. Then we will re-render the component
and pass down our actual data, to simulate the parent
component receiving data from the API and passing that data
down to this child component.
</p>
<p>
<em
>Note that this means we don’t have to test the async
function, or even the event that kicked off the API call. We
just render what this component looks like when it first
mounts with no data, and what it looks like when it receives
new props and re-renders.</em
>
</p>
<ol>
<li>
Create test and pull in relevant matchers from react testing
library.
</li>
</ol>
<div class="language-jsx highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="c1">//import libraries</span>
<span class="k">import</span> <span class="nx">React</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="p">{</span> <span class="nx">render</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">@testing-library/react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="nx">DoggoImages</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">./DoggoImages</span><span class="dl">"</span><span class="p">;</span>
<span class="nx">test</span><span class="p">(</span><span class="dl">"</span><span class="s2">renders dog images from API</span><span class="dl">"</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="c1">// Render the component with an empty array</span>
<span class="kd">const</span> <span class="p">{</span> <span class="nx">getAllByTestId</span><span class="p">,</span> <span class="nx">rerender</span> <span class="p">}</span> <span class="o">=</span> <span class="nx">render</span><span class="p">(<</span><span class="nc">Doggos</span> <span class="na">images=</span><span class="si">{</span><span class="p">[]</span><span class="si">}</span> <span class="p">/>);</span>
<span class="c1">// Assert that there are no dog images rendered yet</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">getAllByTestId</span><span class="p">(</span><span class="sr">/doggo images/i</span><span class="p">)).</span><span class="nx">toHaveLength</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<ol>
<li>
Update prop by passing a user input. Test updated prop using
<code class="highlighter-rouge">rerender</code>.
</li>
</ol>
<div class="language-jsx highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="c1">//import libraries</span>
<span class="k">import</span> <span class="nx">React</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="p">{</span> <span class="nx">render</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">@testing-library/react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="nx">DoggoImages</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">./DoggoImages</span><span class="dl">"</span><span class="p">;</span>
<span class="nx">test</span><span class="p">(</span><span class="dl">"</span><span class="s2">renders dog images from API</span><span class="dl">"</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="kd">const</span> <span class="nx">doggoUrls</span> <span class="o">=</span> <span class="p">[</span>
<span class="dl">'</span><span class="s1">url-one.jpg</span><span class="dl">'</span><span class="p">,</span> <span class="dl">'</span><span class="s1">url-two.jpeg</span><span class="dl">'</span><span class="p">,</span> <span class="dl">'</span><span class="s1">url-three.jpg</span><span class="dl">'</span>
<span class="p">]</span>
<span class="kd">const</span> <span class="p">{</span> <span class="nx">getAllByTestId</span><span class="p">,</span> <span class="nx">rerender</span> <span class="p">}</span> <span class="o">=</span> <span class="nx">render</span><span class="p">(<</span><span class="nc">DoggoImages</span> <span class="na">images=</span><span class="si">{</span><span class="p">[]</span><span class="si">}</span> <span class="p">/>);</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">getAllByTestId</span><span class="p">(</span><span class="sr">/doggo images/i</span><span class="p">)).</span><span class="nx">toHaveLength</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span>
<span class="c1">// We will rerender the component with our dummy data passed in as the new props</span>
<span class="nx">rerender</span><span class="p">(<</span><span class="nc">DoggoImages</span> <span class="na">images=</span><span class="si">{</span><span class="nx">doggoUrls</span><span class="si">}</span> <span class="p">/>);</span>
<span class="c1">// Assert that we now have dog images rendering!</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">getAllByTestId</span><span class="p">(</span><span class="sr">/doggo images/i</span><span class="p">)).</span><span class="nx">toHaveLength</span><span class="p">(</span><span class="mi">3</span><span class="p">);</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<h5>Challenge</h5>
<p>
Find an example of updating props in a previous project.
Design a test using
<code class="highlighter-rouge">rerender</code> that will
assert one state after the component first renders, and assert
a different state after he component renders again with new
props.
</p>
<hr />
<h4 class="mark mb-3 p-2">
Learn to use mocks in web application tests
</h4>
<p>
Unfortunately our functions don’t live in a vacuum, but have
entanglements with the outer world, such as dependencies on
other modules. Or they might take callbacks as arguments,
which creates the interesting problem of how to test that the
callbacks were invoked and the correct arguments passed. To
handle both these problems we can use Jest’s mock functions.
</p>
<h5>Overview</h5>
<p>
A function in testing may have inconvenient dependencies on
other objects. To isolate the behavior of the function, it’s
often desirable to replace the other objects with mocks that
simulate the behavior of the real objects. Replacing objects
is especially useful if the real objects are impractical to
incorporate into the unit test.
</p>
<p>
Another use of mocks is as “spies” because they let us spy on
the behavior of a function that is called by some other code.
Mock functions can keep track of calls to the function, as
well as the parameters passed in those calls. We can even
define an implementation for the mock, but that’s optional.
Simpler mocks that implement only enough behavior to execute
test code are sometimes called “stubs”.
</p>
<h5>Follow Along</h5>
<p>
Let’s implement a helper function with an uncomfortable
dependency that makes the helper <em>impure</em> (reliant on
something outside of its scope) and, therefore, harder to test
<strong
>(you’ll need to install the
<code class="highlighter-rouge">uuid</code> npm
module)</strong
>.
</p>
<div class="language-javascript highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code> <span class="k">import</span> <span class="nx">uuid</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">uuid</span><span class="dl">"</span><span class="p">;</span>
<span class="k">export</span> <span class="kd">const</span> <span class="nx">makeUser</span> <span class="o">=</span> <span class="p">(</span><span class="nx">firstName</span><span class="p">,</span> <span class="nx">lastName</span><span class="p">)</span> <span class="o">=></span> <span class="p">{</span>
<span class="k">return</span> <span class="p">{</span>
<span class="na">id</span><span class="p">:</span> <span class="nx">uuid</span><span class="p">(),</span>
<span class="na">fullName</span><span class="p">:</span> <span class="s2">`</span><span class="p">${</span><span class="nx">firstName</span><span class="p">}</span><span class="s2"> </span><span class="p">${</span><span class="nx">lastName</span><span class="p">}</span><span class="s2">`</span>
<span class="p">};</span>
<span class="p">};</span>
</code></pre>
</div>
</div>
<ol>
<li>
<p>
Testing expected output against actual output would be
hard, because
<code class="highlighter-rouge">uuid()</code> generates a
new, random id each time. We can give it a try, though.
Note the use of
<code class="highlighter-rouge">.toEqual()</code> to make
our assertion. It compares nested properties of objects,
which we need to check here.
</p>
<div class="language-javascript highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="k">import</span> <span class="p">{</span> <span class="nx">makeUser</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">../utils/makeUser</span><span class="dl">"</span><span class="p">;</span>
<span class="nx">test</span><span class="p">(</span><span class="dl">"</span><span class="s2">generates a user with an id and a full name</span><span class="dl">"</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="c1">// Arrange</span>
<span class="kd">const</span> <span class="nx">expected</span> <span class="o">=</span> <span class="p">{</span> <span class="na">id</span><span class="p">:</span> <span class="dl">"</span><span class="s2">abcde</span><span class="dl">"</span><span class="p">,</span> <span class="na">fullName</span><span class="p">:</span> <span class="dl">"</span><span class="s2">Peter Parker</span><span class="dl">"</span> <span class="p">};</span> <span class="c1">// fishy...</span>
<span class="c1">// Act</span>
<span class="kd">const</span> <span class="nx">actual</span> <span class="o">=</span> <span class="nx">makeUser</span><span class="p">(</span><span class="dl">"</span><span class="s2">Peter</span><span class="dl">"</span><span class="p">,</span> <span class="dl">"</span><span class="s2">Parker</span><span class="dl">"</span><span class="p">);</span>
<span class="c1">// Assert</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">actual</span><span class="p">).</span><span class="nx">toEqual</span><span class="p">(</span><span class="nx">expected</span><span class="p">);</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<p>
<img
src="https://tk-assets.lambdaschool.com/6db480a0-84b6-4210-91a2-091475a1c731_ScreenShot2019-04-16at19.33.30.png"
alt="alt text"
/>
</p>
</li>
</ol>
<p>
<em
>By the way, this kind of test is called a
<strong>unit test</strong> - a test for a single unit of
code, like an isolated function like
<code class="highlighter-rouge">makeUser</code>. You’ll
learn more about unit testing in the backend unit, but we
can see what happening here with the AAA framework.</em
>
</p>
<ol>
<li>
<p>
To get around this problem, we can stub out (create) a
fake version of
<code class="highlighter-rouge">uuid</code> that will
replace the real one during the execution of the test.
Outside of the
<code class="highlighter-rouge">test</code> block, at the
top level of the test file, place the following code:
</p>
<div class="language-javascript highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="nx">jest</span><span class="p">.</span><span class="nx">mock</span><span class="p">(</span><span class="dl">"</span><span class="s2">uuid</span><span class="dl">"</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">()</span> <span class="o">=></span> <span class="dl">"</span><span class="s2">abcde</span><span class="dl">"</span><span class="p">);</span>
</code></pre>
</div>
</div>
</li>
</ol>
<p>
Let’s break it down. As the first argument to
<code class="highlighter-rouge">jest.mock()</code>, we pass
the path to the module we want to replace. As the second
argument, we pass a callback that <em>returns</em> whatever it
is <em>we want the faked thing to be</em>. We wish for
<code class="highlighter-rouge">uuid</code> to become a silly
stub function that always returns the same string:
<code class="highlighter-rouge">uuid() // "abcde"</code>. Our
tests should be passing now!
</p>
<h5>Challenge</h5>
<p>
There is a way to centralize mocks that are used often (think
<code class="highlighter-rouge">uuid</code>, or
<code class="highlighter-rouge">axios</code>) in external
files, so that they are used in test suites without even
bothering with imports. Go to the Jest docs and see if you can
find out how!
</p>
<hr />
<h4 class="mark mb-3 p-2">
Learn to test asynchronous API calls that are made in a
component
</h4>
<p>
Most real world applications need to deal with asynchronous
operations. Adding tests to asynchronous code is challenging
as we need to make sure the code has finished executing and
the application is stable before running the assertions.
</p>
<h5>Overview</h5>
<p>
An asynchronous test is a special kind of test that does not
complete right away, as it needs to wait for the results of
one or more asynchronous operations. When writing asynchronous
code, like when dealing with APIs, it’s important to write
asynchronous tests because other tests won’t work as you
expect.
</p>
<p>
React testing library has a couple of helper functions for us
to write these tests. The
<code class="highlighter-rouge">wait</code> function from
react testing library lets us tell the test that we need to
wait for the async call to finish before continuing our
assertions.
</p>
<p>
As mentioned before, we will also use the
<code class="highlighter-rouge">jest.mock</code> function to
make mocks of the asynchronous functions so we won’t have to
wait for the actual call to be made.
</p>
<p>
In the following tutorial, we’ll walk through an example using
API data. Just like we did with non asynchronous tests, we
need to import components, render components, simulate an
event, and run the test - the difference here is simply a few
added functions to make calls asynchronous.
</p>
<h5>Follow Along</h5>
<p>
Let’s say we have a component that fetches data from the
dog.ceo API when the user pushes a “Fetch Doggos” button. The
component uses a function called
<code class="highlighter-rouge">fetchDoggos</code> to make the
API call. We have pulled this function out of the component
and into an
<code class="highlighter-rouge">/api</code> directory in our
file structure to make it easier to test. We would write a
test for this component following these steps:
</p>
<p><strong>Imports</strong></p>
<p>
As usual, we need to
<strong>import the required libraries</strong> for testing. In
addition to our normal libraries, we’ll import
<code class="highlighter-rouge">wait</code> to make our
function run asynchronously, and we’ll import our component
<code class="highlighter-rouge">fetchDoggos</code> as
<code class="highlighter-rouge">mockFetchDoggos</code> so that
we don’t have to wait for the actual call to be made.
</p>
<ul>
<li>
Import the regular
<code class="highlighter-rouge">react</code> and
<code class="highlighter-rouge"
>@testing-library/react</code
>
dependencies
</li>
<li>
Also import <code class="highlighter-rouge">wait</code> from
rtl
</li>
<li>
Import
<code class="highlighter-rouge">fetchDoggos</code> from the
<code class="highlighter-rouge">/api</code> directory, and
rename it to
<code class="highlighter-rouge">mockFetchDoggos</code> so we
know that it will be mocked - remember that a mock allows us
to isolate a function from its dependencies.
</li>
</ul>
<div class="language-jsx highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="c1">// import libraries</span>
<span class="k">import</span> <span class="nx">React</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="p">{</span> <span class="nx">render</span><span class="p">,</span> <span class="nx">fireEvent</span><span class="p">,</span> <span class="nx">waitFor</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">@testing-library/react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="p">{</span> <span class="nx">fetchDoggos</span> <span class="k">as</span> <span class="nx">mockFetchDoggos</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">../api/fetchDoggos</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="nx">Doggos</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">./Doggos</span><span class="dl">"</span><span class="p">;</span>
<span class="c1">// set up test</span>
<span class="nx">test</span><span class="p">(</span><span class="dl">"</span><span class="s2">renders dog images from API</span><span class="dl">"</span><span class="p">,</span> <span class="k">async</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{});</span>
</code></pre>
</div>
</div>
<p><strong>Mocking the Async Function</strong></p>
<p>
Next we need to <strong>set up the mock</strong>. Like before,
we will create the mock outside of the
<code class="highlighter-rouge">test</code> block to mock the
fetchDoggos async function. Then, inside the
<code class="highlighter-rouge">test</code> block we will tell
the mock function with what data it should resolve. When the
component makes the async request using our mocked function,
it will resolve quickly with that data.
</p>
<div class="language-jsx highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="c1">// import libraries</span>
<span class="k">import</span> <span class="nx">React</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="p">{</span> <span class="nx">render</span><span class="p">,</span> <span class="nx">fireEvent</span><span class="p">,</span> <span class="nx">waitFor</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">@testing-library/react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="p">{</span> <span class="nx">fetchDoggos</span> <span class="k">as</span> <span class="nx">mockFetchDoggos</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">../api/fetchDoggos</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="nx">Doggos</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">./Doggos</span><span class="dl">"</span><span class="p">;</span>
<span class="c1">//create mock *before* setting up test</span>
<span class="nx">jest</span><span class="p">.</span><span class="nx">mock</span><span class="p">(</span><span class="dl">"</span><span class="s2">../ap/fetchDoggosi</span><span class="dl">"</span><span class="p">);</span>
<span class="c1">// set up test</span>
<span class="nx">test</span><span class="p">(</span><span class="dl">"</span><span class="s2">renders dog images from API</span><span class="dl">"</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="c1">//mock resolved results</span>
<span class="nx">mockFetchDoggos</span><span class="p">.</span><span class="nx">mockResolvedValueOnce</span><span class="p">({</span>
<span class="na">message</span><span class="p">:</span> <span class="p">[</span>
<span class="dl">"</span><span class="s2">https://images.dog.ceo/breeds/hound-afghan/n02088094_1003.jpg</span><span class="dl">"</span><span class="p">,</span>
<span class="dl">"</span><span class="s2">https://images.dog.ceo/breeds/hound-afghan/n02088094_1007.jpg</span><span class="dl">"</span><span class="p">,</span>
<span class="dl">"</span><span class="s2">https://images.dog.ceo/breeds/hound-afghan/n02088094_1023.jpg</span><span class="dl">"</span>
<span class="p">]</span>
<span class="p">});</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<p><strong>Render, Query, and Fire Events</strong></p>
<p>
Render the component, query for the necessary elements, and
fire the onClick event with
<code class="highlighter-rouge">fireEvent</code>. This step
should look familiar from our first lessons on react testing
library as we haven’t added any of the async functionality yet
(other than importing
<code class="highlighter-rouge">wait</code>).
</p>
<div class="language-jsx highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="c1">//import libraries</span>
<span class="k">import</span> <span class="nx">React</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="p">{</span> <span class="nx">render</span><span class="p">,</span> <span class="nx">fireEvent</span><span class="p">,</span> <span class="nx">waitFor</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">@testing-library/react</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="p">{</span> <span class="nx">fetchDoggos</span> <span class="k">as</span> <span class="nx">mockFetchDoggos</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">../api/fetchDoggos</span><span class="dl">"</span><span class="p">;</span>
<span class="k">import</span> <span class="nx">Doggos</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">./Doggos</span><span class="dl">"</span><span class="p">;</span>
<span class="c1">//set up test</span>