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<h4 class="bd-toc-link">Web Applications II</h4>
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Class Components
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The React Lifecycle
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Composing and Sharing Non-Visual Behavior
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Testing Web Applications
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The Reducer Pattern
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Async Redux
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Context API
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Testing React
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HTTP / AJAX II
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Deploying Web Apps
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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"
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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>
</div>
<div class="bd-toc-item">
<a class="bd-toc-link" href="/web3/sprint/recq59MvEIZfUAohy">
1. Advanced React
</a>
<ul class="nav bd-sidenav">
<li>
<a href="/web3/module/recnDKrWb24lgaziC/">
Class Components
</a>
</li>
<li>
<a href="/web3/module/rec1DPoOZSmocXfak/">
The React Lifecycle
</a>
</li>
<li>
<a href="/web3/module/recAxmnYmusEi8JuL/">
Composing and Sharing Non-Visual Behavior
</a>
</li>
<li class="active bd-sidenav-active">
<a href="/web3/module/rechTQVfCg4p85Hoi/">
Testing Web Applications
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<a class="bd-toc-link" href="/web3/sprint/recukritK1B1pFrcM">
2. Advanced State Management
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<li>
<a href="/web3/module/rectpk6uIV3pCHJh8/">
The Reducer Pattern
</a>
</li>
<li>
<a href="/web3/module/recba2NUdVmgKYyR3/"> Redux </a>
</li>
<li>
<a href="/web3/module/recSoiWNJzGURrXYh/"> Async Redux </a>
</li>
<li>
<a href="/web3/module/recByjgF7FwwH5Z7W/"> Context API </a>
</li>
</ul>
</div>
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<a class="bd-toc-link" href="/web3/sprint/recnhsJGy28gNi1K5">
3. Advanced Web Applications
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<li>
<a href="/web3/module/recS9H6qCj0dQe32B/">
Testing React
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</li>
<li>
<a href="/web3/module/recQlbCZf9tOVgiXC/">
Client-Side Authentication
</a>
</li>
<li>
<a href="/web3/module/recupVjaAKPqbuk7Y/">
HTTP / AJAX II
</a>
</li>
<li>
<a href="/web3/module/receOMvCB7dSyX5FL/">
Deploying Web Apps
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<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>
<li class="toc-entry toc-h2"><a href="#review">Review</a></li>
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<h1 class="bd-title" id="content">
Testing Web Applications
</h1>
<span class="lead">
<p class="bd-lead"></p>
<p>
In this module we will learn about automated testing, and
more specifically how to write unit tests with Jest and
react-testing-library.
</p>
</span>
<strong
>At the end of this module, you should be able to:</strong
>
<ul>
<li>
explain what automated testing is and its importance
</li>
<li>
use react-testing-library for testing react components
</li>
<li>
use react-testing-library to test user interactions with
fireEvent
</li>
</ul>
</div>
<div class="alert alert-warning" role="alert">
<h4>Pro Tip</h4>
<p>We all build on the work of others.</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">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/jyWUNzzV29U"
frameborder="0"
allowfullscreen
></iframe>
</div>
</li>
<li class="list-group-item">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/uFXGcLpbBMU"
frameborder="0"
allowfullscreen
></iframe>
</div>
</li>
<li class="list-group-item">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/vItkiDBCVcc"
frameborder="0"
allowfullscreen
></iframe>
</div>
</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 explain what automated testing is and its importance
</h4>
<p>
Testing is essential for software quality. It should be
integrated into the development process from beginning to end.
We should not wait until a feature is complete to start
testing it. Testing software manually on every commit to
source control or every time we make a change does not scale!
Automated testing works by using software to test our code.
</p>
<h5>Overview</h5>
<h3 id="why-test">Why test</h3>
<p>
Automated testing minimizes the risk of bugs finding their way
into production code.
<strong>Testing is NOT optional</strong>. Testing should be a
part of every developer’s workflow. A feature is not done
until it is fully tested! In direct contrast to manual
testing, automated testing significantly reduces the manpower
and margin for error needed to confidently ship a product.
Though it can’t entirely remove manual testing from the
process, it certainly helps.
</p>
<p><strong>In terms of benefits, testing…</strong></p>
<ul>
<li>Surfaces bugs faster.</li>
<li>Reduces the risk of regressions.</li>
<li>Allows us to trust the code.</li>
<li>Makes us think about the edge cases.</li>
<li>
Acts as a safety net when making changes or refactoring.
</li>
<li>Acts as documentation for the code.</li>
<li>Encourages us to write more testable (better!) code.</li>
</ul>
<p><strong>On the other hand, NOT testing…</strong></p>
<ul>
<li>Forces very expensive manual testing.</li>
<li>Causes bugs and edge cases to be encountered later.</li>
<li>Makes refactoring or adding features risky and scary.</li>
<li>Can make codebases fragile and expensive to maintain.</li>
<li>
Makes less documented codebases much harder to understand.
</li>
</ul>
<p>
Not writing tests can be thought of as
<strong>taking a loan with a very high-interest rate</strong>.
The quick payoff is being able to write spaghetti code
unhindered. The costs long term can become enormous and
surpass hundreds of times over any marginal time gains
obtained by not writing tests. Eventually, entire teams of
developers can get so bogged down in bugs and regressions that
the product can’t move forward.
</p>
<h3 id="types-of-testing">Types of testing</h3>
<p>
There are many different ways of classifying tests. Here are
some common levels of testing:
</p>
<h4 id="integration-testing">Integration testing</h4>
<p>
In this level, several units of software are tested as a group
to ensure they work together correctly.
</p>
<h4 id="end-to-end-testing">End-to-end testing</h4>
<p>
End-to-end (E2E) testing is where the whole application is
tested, simulating real user scenarios closely. Because these
tests are slow and expensive, there should be a thick
“cushion” of unit tests in a codebase.
</p>
<h4 id="unit-testing">Unit Testing</h4>
<p>
We test the smaller units of software (often functions or
methods) in isolation. There are usually many unit tests in a
codebase, and because these tests are meant to be run often,
they need to run fast. We will talk about this eventually, but
not much today.
</p>
<h3 id="when-to-test">When to Test</h3>
<p>
When trying to determine whether to manually test a feature,
or to automate testing, consider the following guidelines:
</p>
<ul>
<li>
Automated testing should be built for any test that is
executed often. Internally at Lambda we say “1..2..
automate!” meaning, you should only do a task 2 times
manually before you are required to build out a system to
automate that test or task for you. It isn’t always
relevant, but a catchy motto to consider.
</li>
<li>
Automated testing should be built for any difficult manual
task - if it requires too much work, or too many steps, that
even a 2nd manual test would be a large task, automate it
from the start.
</li>
<li>
Automated testing should be built for any test that, if it
fails, will dramatically affect the use of a product or
health of a company. For example, you’d always want to build
a test to check for security of credit card information on a
payment processing website.
</li>
</ul>
<p>
On the flip side, if you’re trying something new, or if test
requirements are changing a lot, you can probably hold off on
creating an automated test.
</p>
<h3 id="how-to-test">How to Test</h3>
<p>
The framework we use for testing is: arrange, act, assert.
These are three steps that we can take to build good tests.
First, we “arrange” our test by setting up our code such that
it can be tested. Then, we “act” - calling a method or
function that returns a result of interest to our test.
Finally, with that return we “assert” if our expected return
matched the actual return.
</p>
<p>
Very often arrange and act will happen in the same line of
code, for illustration here we’ve separated these sections,
but don’t be scared if you see them together.
</p>
<h5>Follow Along</h5>
<p>
Read through this article that talks about how to know what to
test: https://kentcdodds.com/blog/how-to-know-what-to-test
</p>
<h5>Challenge</h5>
<p>
Research other types of tests: sanity testing, smoke testing,
regression testing, system testing, snapshot testing,
acceptance testing.
</p>
<hr />
<h4 class="mark mb-3 p-2">
Learn to use react-testing-library for testing react
components
</h4>
<p>
In the Node ecosystem, small and specialized libraries prevail
over large, batteries-included frameworks. In a similar way
architecting a React application requires putting together a
stack made of several different libraries, testing our React
components require that we choose libraries depending on the
methodology we favor, and use them together.
</p>
<h5>Overview</h5>
<p>
In the last objective we discussed the general
<em>what</em> and <em>why</em> of testing. Here we’re going to
dive into the <em>how</em>. We will use the
<a
href="https://testing-library.com/docs/react-testing-library/intro"
>react-testing-library</a
>
to run tests in this unit. Unlike previous testing libraries,
react-testing-library is designed with the user in mind,
testing components via DOM nodes, similar to how a user would
interact with the front end of a website.
</p>
<p>
react-testing-library recently underwent a major overhaul - we
used to use a different libraries, Enzyme and Jest, for tests
that cared more about the internal management of props and
state. Now though, we can use react-testing-library to test
prop, state, output (in DOM elements), and more.
</p>
<p>
The “hello world” so to speak in the react-testing-library is
a test to check if a component loads without crashing. Here,
we declare a test, name it, and check if the App renders.
</p>
<div class="language-js 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">renders App without crashing</span><span class="dl">"</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="nx">render</span><span class="p">(</span><span class="o"><</span><span class="nx">App</span> <span class="o">/></span><span class="p">);</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<p>
Earlier, we discussed about the “Arrange, Act, Assert”
structure for testing. There’s a technical first step, import
- we’ll look at all of them below. For more details, check out
the
<a
href="https://testing-library.com/docs/react-testing-library/example-intro"
>testing-library documentation</a
>.
</p>
<p>
The following matches the structure we’ve studied and is
slightly simplified version of what you’‘ll find in the
documentation. What we’ll walk through in the tutorial is even
more simple but this example is good for illustration.
</p>
<p>
Here we are testing the
<code class="highlighter-rouge">greeting</code> component to
see if our expected greeting (“hello lambdalorians”) appears
in the browser as we expect it will per the code below.
Important note here, our tests work with text because that’s
what the user sees and what the user experiences - the test
does not test on classes, for example, because that’s an
implementation detail, not a rendered element.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="k">import</span> <span class="nx">React</span> <span class="k">from</span> <span class="dl">'</span><span class="s1">react</span><span class="dl">'</span><span class="p">;</span>
<span class="kd">const</span> <span class="nx">Greeting</span> <span class="o">=</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="k">return</span> <span class="o"><</span><span class="nx">h1</span> <span class="kd">class</span><span class="o">=</span><span class="dl">"</span><span class="s2">my-greeting</span><span class="dl">"</span><span class="o">></span><span class="nx">Hello</span> <span class="nx">Lambdalorians</span><span class="o">!<</span><span class="sr">/h1></span><span class="err">;
</span><span class="p">};</span>
<span class="k">export</span> <span class="k">default</span> <span class="nx">Greeting</span><span class="p">;</span>
</code></pre>
</div>
</div>
<h3 id="import">Import</h3>
<p>
As with any library, we need to import react-testing-library
before we can use it, this all should look more or less
familiar from imports we’ve done before. You’ll notice that
“Arrange, Act, and Assert” are yet to be filled out.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="c1">// import dependencies</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="c1">// import react-testing methods</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="c1">// add greeting</span>
<span class="k">import</span> <span class="nx">Greeting</span> <span class="k">from</span> <span class="dl">"</span><span class="s2">./Greeting</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 greeting on Greeting component</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>
<span class="c1">// Arrange</span>
<span class="c1">// Act</span>
<span class="c1">// Assert</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<h3 id="arrange">Arrange</h3>
<p>
The <code class="highlighter-rouge">render</code> method
renders a React element into a virtual DOM and returns utility
functions for testing the component. Recalling our definition
of “arrange”, this is basically the part where we set
ourselves up for success. Here, we use
<code class="highlighter-rouge">getByText</code> to set up the
action that we want to run later on - checking the greeting
text.
</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">renders greeting on Greeting component</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>
<span class="c1">// Arrange</span>
<span class="kd">const</span> <span class="p">{</span> <span class="nx">getByText</span> <span class="p">}</span> <span class="o">=</span> <span class="nx">render</span><span class="p">(<</span><span class="nc">Greeting</span> <span class="p">/>);</span>
<span class="c1">// Act</span>
<span class="c1">// Assert</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<h3 id="act">Act</h3>
<p>
The <code class="highlighter-rouge">getByText</code> method
can be used to “query” the DOM for a specific node by its text
that we expect to see in the browser. We will use it here to
test that our greeting (“hello lambdalorians”) is being
rendered by the
<code class="highlighter-rouge"><Greeting /></code>
component.
</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">renders greeting on Greeting component</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>
<span class="c1">// Arrange</span>
<span class="kd">const</span> <span class="p">{</span> <span class="nx">getByText</span> <span class="p">}</span> <span class="o">=</span> <span class="nx">render</span><span class="p">(<</span><span class="nc">Greeting</span> <span class="p">/>);</span>
<span class="c1">// Act</span>
<span class="kd">const</span> <span class="nx">greeting</span> <span class="o">=</span> <span class="nx">getByText</span><span class="p">(</span><span class="sr">/hello lambdalorians!/i</span><span class="p">);</span>
<span class="c1">// Assert</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<p>
A quick note here, you may notice that “hello lambdalorians”
is written with
<code class="highlighter-rouge">/</code> instead of
<code class="highlighter-rouge">"</code>s. This is regex
syntax and is commonly used in testing. the
<code class="highlighter-rouge">i</code> designates our text
as case insensitive so even though we have the string “hello
lambdalorians” written, our test will pass even if “hElLo
LamBdAlOriAns” is displayed in the browser.
</p>
<h3 id="assert">Assert</h3>
<p>
Finally, we need to “assert” that the greeting has indeed been
rendered. Here we use a couple of new functions -
<code class="highlighter-rouge">expect</code> is a Jest
function that is made globally available with create react
app. The other,
<code class="highlighter-rouge">toBeInTheDocument()</code>,
comes from
<a href="https://testing-library.com/docs/ecosystem-jest-dom"
>Jest DOM</a
>, a companion library to react-testing-library that provides
custom matchers for Jest. A full list of functions can be
found on
<a href="https://github.com/testing-library/jest-dom"
>GitHub</a
>. Throughout our examples we assume that you import Jest DOM
in create-react-app, and suggest that you always do this,
rather than importing it every time.
</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">renders greeting on Greeting component</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>
<span class="c1">// Arrange</span>
<span class="kd">const</span> <span class="p">{</span> <span class="nx">getByText</span> <span class="p">}</span> <span class="o">=</span> <span class="nx">render</span><span class="p">(<</span><span class="nc">Greeting</span> <span class="p">/>);</span>
<span class="c1">// Act</span>
<span class="kd">const</span> <span class="nx">greeting</span> <span class="o">=</span> <span class="nx">getByText</span><span class="p">(</span><span class="sr">/hello lambdalorians!/i</span><span class="p">);</span>
<span class="c1">// Assert</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">greeting</span><span class="p">).</span><span class="nx">toBeInTheDocument</span><span class="p">();</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<h3 id="running-tests">Running Tests</h3>
<p>
You should be at least somewhat familiar with this process
from tests that we’ve used throughout Lambda to help your code
along. All tests run in the terminal with
<code class="highlighter-rouge">npm test</code> - as you run
tests you should see passes and failures in the console.
Running this test would result in a “pass” since our earlier
code does indeed render “Hello Lambdalorians”.
</p>
<h5>Follow Along</h5>
<p>
Here, we are testing to see wither learn react will render the
way we expect it to.
</p>
<ol>
<li>
<strong>Create a React project</strong> with
<code class="highlighter-rouge">create-react-app</code> in
command line.
</li>
</ol>
<p>
Remember that older versions of Create React App required you
to install
<code class="highlighter-rouge"
>@testing-library/jest-dom</code
>
and
<code class="highlighter-rouge">@testing-library/react</code>
separately. Not anymore. And
<strong>we do NOT need to install Jest</strong> either, as CRA
projects come with Jest installed and working out of the box.
</p>
<ol>
<li>
<strong
>Open
<code class="highlighter-rouge">App.test.js</code></strong
>
(inside the
<code class="highlighter-rouge">src</code> folder). You
should see the below:
</li>
</ol>
<div class="language-javascript highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code> <span class="k">import</span> <span class="nx">React</span> <span class="k">from</span> <span class="dl">'</span><span class="s1">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="s1">@testing-library/react</span><span class="dl">'</span><span class="p">;</span>
<span class="k">import</span> <span class="nx">App</span> <span class="k">from</span> <span class="dl">'</span><span class="s1">./App</span><span class="dl">'</span><span class="p">;</span>
<span class="nx">test</span><span class="p">(</span><span class="dl">'</span><span class="s1">renders learn react link</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="p">{</span> <span class="nx">getByText</span> <span class="p">}</span> <span class="o">=</span> <span class="nx">render</span><span class="p">(</span><span class="o"><</span><span class="nx">App</span> <span class="o">/></span><span class="p">);</span>
<span class="kd">const</span> <span class="nx">linkElement</span> <span class="o">=</span> <span class="nx">getByText</span><span class="p">(</span><span class="sr">/learn react/i</span><span class="p">);</span>
<span class="nx">expect</span><span class="p">(</span><span class="nx">linkElement</span><span class="p">).</span><span class="nx">toBeInTheDocument</span><span class="p">();</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<ol>
<li><strong>Note</strong> a few things about the imports:</li>
</ol>
<ul>
<li>
<code class="highlighter-rouge">React</code> has to be in
scope because we will be using JSX.
</li>
<li>
<code class="highlighter-rouge">react-testing-library</code>
exposes a render function that we are importing with
<code class="highlighter-rouge">import { render }</code>
syntax. This allows us to render React components so we can
<strong>test them</strong>.
</li>
</ul>
<ol>
<li>
<strong>Render a React element</strong> containing a “Hello
World” message, and run tests as usual:
</li>
</ol>
<div class="language-javascript highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code> <span class="nx">it</span><span class="p">(</span><span class="dl">'</span><span class="s1">renders without crashing</span><span class="dl">'</span><span class="p">,</span> <span class="p">()</span> <span class="o">=></span> <span class="p">{</span>
<span class="nx">render</span><span class="p">(</span>
<span class="o"><</span><span class="nx">span</span> <span class="nx">className</span><span class="o">=</span><span class="dl">"</span><span class="s2">greet</span><span class="dl">"</span><span class="o">></span><span class="nx">hello</span> <span class="nx">world</span><span class="o"><</span><span class="sr">/span</span><span class="err">>
</span> <span class="p">);</span>
<span class="p">});</span>
</code></pre>
</div>
</div>
<ol>
<li>
<strong>Inspect the output</strong> by logging
<code class="highlighter-rouge">wrapper.debug()</code>. See
how the element is rendered into a in-memory document-like
structure:
</li>
</ol>
<p>
<img
src="https://tk-assets.lambdaschool.com/f9be6244-1d0a-4386-ae0e-cf01e20b98f7_ScreenShot2019-04-15at13.56.43.png"
alt="alt text"
/>
</p>
<ol>
<li>
<strong>Capture the node of interest.</strong> Let’s assume
the true, actual purpose of some React component returning
the jsx
<code class="highlighter-rouge"
><span>hello world</span></code
>
is to render a “hello” message to the screen for the user to
see. We could assert that by mounting such a component, the
browser will render a span containing this language. We can
use a
<code class="highlighter-rouge">dom-testing-library</code>
<strong>query</strong> to capture such an element:
</li>
</ol>
<div class="language-javascript highlighter-rouge">