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<meta property="og:description" content="When writing RNTL tests one of the things that confuses developers the most are cryptic act() function errors logged into console. In this article I will try to build an understanding of the purpose and behaviour of act() so you can build your tests with more confidence.">
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<meta name="description" content="When writing RNTL tests one of the things that confuses developers the most are cryptic act() function errors logged into console. In this article I will try to build an understanding of the purpose and behaviour of act() so you can build your tests with more confidence."></head>
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rp-link" style="padding-left:calc(12px * 2 + 12px)" data-depth="2"><div class="rp-sidebar-item__left"><span>v2</span></div><div class="rp-sidebar-item__right"></div></a></div></div></div></div></aside><div class="rp-doc-layout__doc"><main class="rp-doc-layout__doc-container"><div class="rp-doc rspress-doc"><!--$--><h1 class="rp-toc-include" id="understanding-act-function"><a href="#understanding-act-function" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Understanding <code>act</code> function<!-- --> </h1><div class="rp-not-doc rp-llms-container"><button class="rp-not-doc rp-llms-button rp-llms-copy-button"><div class="rp-llms-copy-button__icon-wrapper"><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-llms-copy-button__icon-success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-llms-copy-button__icon-copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg></div><span>Copy Markdown</span></button><button class="rp-llms-button rp-llms-view-options__trigger "><svg xmlns="http://www.w3.org/2000/svg" width="12" height="13" viewBox="0 0 12 13" class="rp-llms-view-options__arrow "><path fill="currentColor" d="M6.5 8.5h1v1h-1v1h-1v-1h-1v-1h1v-6h1zm-2 0h-1v-1h1zm4 0h-1v-1h1zm-5-2v1h-1v-1zm6 1h-1v-1h1z"></path></svg></button></div>
<p>When writing RNTL tests one of the things that confuses developers the most are cryptic <a href="https://reactjs.org/docs/testing-recipes.html#act" target="_blank" rel="noopener noreferrer" class="rp-link"><code>act()</code></a> function errors logged into console. In this article I will try to build an understanding of the purpose and behaviour of <code>act()</code> so you can build your tests with more confidence.</p>
<h2 class="rp-toc-include" id="act-warnings"><a href="#act-warnings" class="rp-header-anchor rp-link" aria-hidden="true">#</a><code>act</code> warnings</h2>
<p>Let’s start with typical <code>act()</code> warnings logged to console. There are two kinds of these issues, let’s call the first one the &quot;sync <code>act()</code>&quot; warning:</p>
<div class="rp-codeblock language-txt"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="txt"><code><span class="line"><span>Warning: An update to Component inside a test was not wrapped in act(...).</span></span>
<span class="line"><span></span></span>
<span class="line"><span>When testing, code that causes React state updates should be wrapped into act(...):</span></span>
<span class="line"><span></span></span>
<span class="line"><span>act(() =&gt; {</span></span>
<span class="line"><span> /* fire events that update state */</span></span>
<span class="line"><span>});</span></span>
<span class="line"><span>/* assert on the output */</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>The second one relates to async usage of <code>act</code> so let’s call it the &quot;async <code>act</code>&quot; error:</p>
<div class="rp-codeblock language-txt"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="txt"><code><span class="line"><span>Warning: You called act(async () =&gt; ...) without await. This could lead to unexpected</span></span>
<span class="line"><span>testing behaviour, interleaving multiple act calls and mixing their scopes. You should</span></span>
<span class="line"><span>- await act(async () =&gt; ...);</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<h2 class="rp-toc-include" id="synchronous-act"><a href="#synchronous-act" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Synchronous <code>act</code></h2>
<h3 class="rp-toc-include" id="responsibility"><a href="#responsibility" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Responsibility</h3>
<p>This function is intended only for using in automated tests and works only in development mode. Attempting to use it in production build will throw an error.</p>
<p>The responsibility for <code>act</code> function is to make React renders and updates work in tests in a similar way they work in real application by grouping and executing related units of interaction (e.g. renders, effects, etc) together.</p>
<p>To showcase that behaviour let make a small experiment. First we define a function component that uses <code>useEffect</code> hook in a trivial way.</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-keyword)">function</span><span style="color:var(--shiki-token-function)"> TestComponent</span><span style="color:var(--shiki-foreground)">() {</span></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> const</span><span style="color:var(--shiki-foreground)"> [</span><span style="color:var(--shiki-token-constant)">count</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-token-constant)"> setCount</span><span style="color:var(--shiki-foreground)">] </span><span style="color:var(--shiki-token-keyword)">=</span><span style="color:var(--shiki-token-constant)"> React</span><span style="color:var(--shiki-token-function)">.useState</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">0</span><span style="color:var(--shiki-foreground)">);</span></span>
<span class="line"><span style="color:var(--shiki-token-constant)"> React</span><span style="color:var(--shiki-token-function)">.useEffect</span><span style="color:var(--shiki-foreground)">(() </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> setCount</span><span style="color:var(--shiki-foreground)">((c) </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> c </span><span style="color:var(--shiki-token-keyword)">+</span><span style="color:var(--shiki-token-constant)"> 1</span><span style="color:var(--shiki-foreground)">);</span></span>
<span class="line"><span style="color:var(--shiki-foreground)"> }</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-foreground)"> []);</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> return</span><span style="color:var(--shiki-foreground)"> &lt;</span><span style="color:var(--shiki-token-constant)">Text</span><span style="color:var(--shiki-foreground)">&gt;Count {count}&lt;/</span><span style="color:var(--shiki-token-constant)">Text</span><span style="color:var(--shiki-foreground)">&gt;;</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">}</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>In the following tests we will directly use <code>ReactTestRenderer</code> instead of RNTL <code>render</code> function to render our component for tests. In order to expose familiar queries like <code>getByText</code> we will use <code>within</code> function from RNTL.</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-function)">test</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;render without act&#x27;</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> const</span><span style="color:var(--shiki-token-constant)"> renderer</span><span style="color:var(--shiki-token-keyword)"> =</span><span style="color:var(--shiki-token-constant)"> TestRenderer</span><span style="color:var(--shiki-token-function)">.create</span><span style="color:var(--shiki-foreground)">(&lt;</span><span style="color:var(--shiki-token-constant)">TestComponent</span><span style="color:var(--shiki-foreground)"> /&gt;);</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-comment)"> // Bind RNTL queries for root element.</span></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> const</span><span style="color:var(--shiki-token-constant)"> view</span><span style="color:var(--shiki-token-keyword)"> =</span><span style="color:var(--shiki-token-function)"> within</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">renderer</span><span style="color:var(--shiki-foreground)">.root);</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> expect</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">view</span><span style="color:var(--shiki-token-function)">.getByText</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;Count 0&#x27;</span><span style="color:var(--shiki-foreground)">))</span><span style="color:var(--shiki-token-function)">.toBeOnTheScreen</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">});</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>When testing without <code>act</code> call wrapping rendering call, we see that the assertion runs just after the rendering but before <code>useEffect</code>hooks effects are applied. Which is not what we expected in our tests.</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-function)">test</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;render with act&#x27;</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> let</span><span style="color:var(--shiki-foreground)"> renderer</span><span style="color:var(--shiki-token-keyword)">:</span><span style="color:var(--shiki-token-function)"> ReactTestRenderer</span><span style="color:var(--shiki-foreground)">;</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> act</span><span style="color:var(--shiki-foreground)">(() </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-foreground)"> renderer </span><span style="color:var(--shiki-token-keyword)">=</span><span style="color:var(--shiki-token-constant)"> TestRenderer</span><span style="color:var(--shiki-token-function)">.create</span><span style="color:var(--shiki-foreground)">(&lt;</span><span style="color:var(--shiki-token-constant)">TestComponent</span><span style="color:var(--shiki-foreground)"> /&gt;);</span></span>
<span class="line"><span style="color:var(--shiki-foreground)"> });</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-comment)"> // Bind RNTL queries for root element.</span></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> const</span><span style="color:var(--shiki-token-constant)"> view</span><span style="color:var(--shiki-token-keyword)"> =</span><span style="color:var(--shiki-token-function)"> within</span><span style="color:var(--shiki-foreground)">(renderer</span><span style="color:var(--shiki-token-keyword)">!</span><span style="color:var(--shiki-foreground)">.root);</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> expect</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">view</span><span style="color:var(--shiki-token-function)">.getByText</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;Count 1&#x27;</span><span style="color:var(--shiki-foreground)">))</span><span style="color:var(--shiki-token-function)">.toBeOnTheScreen</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">});</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>When wrapping rendering call with <code>act</code> we see that the changes caused by <code>useEffect</code> hook have been applied as we would expect.</p>
<h3 class="rp-toc-include" id="when-to-use-act"><a href="#when-to-use-act" class="rp-header-anchor rp-link" aria-hidden="true">#</a>When to use act</h3>
<p>The name <code>act</code> comes from <a href="http://wiki.c2.com/?ArrangeActAssert" target="_blank" rel="noopener noreferrer" class="rp-link">Arrange-Act-Assert</a> unit testing pattern. Which means it’s related to part of the test when we execute some actions on the component tree.</p>
<p>So far we learned that <code>act</code> function allows tests to wait for all pending React interactions to be applied before we make our assertions. When using <code>act</code> we get guarantee that any state updates will be executed as well as any enqueued effects will be executed.</p>
<p>Therefore, we should use <code>act</code> whenever there is some action that causes element tree to render, particularly:</p>
<ul>
<li>initial render call - <code>ReactTestRenderer.create</code> call</li>
<li>re-rendering of component -<code>renderer.update</code> call</li>
<li>triggering any event handlers that cause component tree render</li>
</ul>
<p>Thankfully, for these basic cases RNTL has got you covered as our <code>render</code>, <code>update</code> and <code>fireEvent</code> methods already wrap their calls in sync <code>act</code> so that you do not have to do it explicitly.</p>
<p>Note that <code>act</code> calls can be safely nested and internally form a stack of calls. However, overlapping <code>act</code> calls, which can be achieved using async version of <code>act</code>, <a href="https://github.com/facebook/react/blob/main/packages/react/src/ReactAct.js#L161" target="_blank" rel="noopener noreferrer" class="rp-link">are not supported</a>.</p>
<h3 class="rp-toc-include" id="implementation"><a href="#implementation" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Implementation</h3>
<p>As of React version of 18.1.0, the <code>act</code> implementation is defined in the <a href="https://github.com/facebook/react/blob/main/packages/react/src/ReactAct.js" target="_blank" rel="noopener noreferrer" class="rp-link">ReactAct.js source file</a> inside React repository. This implementation has been fairly stable since React 17.0.</p>
<p>RNTL exports <code>act</code> for convenience of the users as defined in the <a href="https://github.com/callstack/react-native-testing-library/blob/main/src/act.ts" target="_blank" rel="noopener noreferrer" class="rp-link">act.ts source file</a>. That file refers to <a href="https://github.com/facebook/react/blob/ce13860281f833de8a3296b7a3dad9caced102e9/packages/react-test-renderer/src/ReactTestRenderer.js#L52" target="_blank" rel="noopener noreferrer" class="rp-link">ReactTestRenderer.js source</a> file from React Test Renderer package, which finally leads to React act implementation in ReactAct.js (already mentioned above).</p>
<h2 class="rp-toc-include" id="asynchronous-act"><a href="#asynchronous-act" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Asynchronous <code>act</code></h2>
<p>So far we have seen synchronous version of <code>act</code> which runs its callback immediately. This can deal with things like synchronous effects or mocks using already resolved promises. However, not all component code is synchronous. Frequently our components or mocks contain some asynchronous behaviours like <code>setTimeout</code> calls or network calls. Starting from React 16.9, <code>act</code> can also be called in asynchronous mode. In such case <code>act</code> implementation checks that the passed callback returns <a href="https://github.com/facebook/react/blob/ce13860281f833de8a3296b7a3dad9caced102e9/packages/react/src/ReactAct.js#L60" target="_blank" rel="noopener noreferrer" class="rp-link">object resembling promise</a>.</p>
<h3 class="rp-toc-include" id="asynchronous-code"><a href="#asynchronous-code" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Asynchronous code</h3>
<p>Asynchronous version of <code>act</code> also is executed immediately, but the callback is not yet completed because of some asynchronous operations inside.</p>
<p>Lets look at a simple example with component using <code>setTimeout</code> call to simulate asynchronous behaviour:</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-keyword)">function</span><span style="color:var(--shiki-token-function)"> TestAsyncComponent</span><span style="color:var(--shiki-foreground)">() {</span></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> const</span><span style="color:var(--shiki-foreground)"> [</span><span style="color:var(--shiki-token-constant)">count</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-token-constant)"> setCount</span><span style="color:var(--shiki-foreground)">] </span><span style="color:var(--shiki-token-keyword)">=</span><span style="color:var(--shiki-token-constant)"> React</span><span style="color:var(--shiki-token-function)">.useState</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">0</span><span style="color:var(--shiki-foreground)">);</span></span>
<span class="line"><span style="color:var(--shiki-token-constant)"> React</span><span style="color:var(--shiki-token-function)">.useEffect</span><span style="color:var(--shiki-foreground)">(() </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> setTimeout</span><span style="color:var(--shiki-foreground)">(() </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> setCount</span><span style="color:var(--shiki-foreground)">((c) </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> c </span><span style="color:var(--shiki-token-keyword)">+</span><span style="color:var(--shiki-token-constant)"> 1</span><span style="color:var(--shiki-foreground)">);</span></span>
<span class="line"><span style="color:var(--shiki-foreground)"> }</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-token-constant)"> 50</span><span style="color:var(--shiki-foreground)">);</span></span>
<span class="line"><span style="color:var(--shiki-foreground)"> }</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-foreground)"> []);</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> return</span><span style="color:var(--shiki-foreground)"> &lt;</span><span style="color:var(--shiki-token-constant)">Text</span><span style="color:var(--shiki-foreground)">&gt;Count {count}&lt;/</span><span style="color:var(--shiki-token-constant)">Text</span><span style="color:var(--shiki-foreground)">&gt;;</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">}</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-keyword)">import</span><span style="color:var(--shiki-foreground)"> { render</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-foreground)"> screen } </span><span style="color:var(--shiki-token-keyword)">from</span><span style="color:var(--shiki-token-string-expression)"> &#x27;@testing-library/react-native&#x27;</span><span style="color:var(--shiki-foreground)">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-function)">test</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;render async natively&#x27;</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> render</span><span style="color:var(--shiki-foreground)">(&lt;</span><span style="color:var(--shiki-token-constant)">TestAsyncComponent</span><span style="color:var(--shiki-foreground)"> /&gt;);</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> expect</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">screen</span><span style="color:var(--shiki-token-function)">.getByText</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;Count 0&#x27;</span><span style="color:var(--shiki-foreground)">))</span><span style="color:var(--shiki-token-function)">.toBeOnTheScreen</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">});</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>If we test our component in a native way without handling its asynchronous behaviour we will end up with sync act warning:</p>
<div class="rp-codeblock language-txt"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="txt"><code><span class="line"><span>Warning: An update to TestAsyncComponent inside a test was not wrapped in act(...).</span></span>
<span class="line"><span></span></span>
<span class="line"><span>When testing, code that causes React state updates should be wrapped into act(...):</span></span>
<span class="line"><span></span></span>
<span class="line"><span>act(() =&gt; {</span></span>
<span class="line"><span> /* fire events that update state */</span></span>
<span class="line"><span>});</span></span>
<span class="line"><span>/* assert on the output */</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>Note that this is not yet the infamous async act warning. It only asks us to wrap our event code with <code>act</code> calls. However, this time our immediate state change does not originate from externally triggered events but rather forms an internal part of the component. So how can we apply <code>act</code> in such scenario?</p>
<h3 class="rp-toc-include" id="solution-with-fake-timers"><a href="#solution-with-fake-timers" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Solution with fake timers</h3>
<p>First solution is to use Jest&#x27;s fake timers inside out tests:</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-function)">test</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;render with fake timers&#x27;</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-constant)"> jest</span><span style="color:var(--shiki-token-function)">.useFakeTimers</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> render</span><span style="color:var(--shiki-foreground)">(&lt;</span><span style="color:var(--shiki-token-constant)">TestAsyncComponent</span><span style="color:var(--shiki-foreground)"> /&gt;);</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-function)"> act</span><span style="color:var(--shiki-foreground)">(() </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-constant)"> jest</span><span style="color:var(--shiki-token-function)">.runAllTimers</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-foreground)"> });</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> expect</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">screen</span><span style="color:var(--shiki-token-function)">.getByText</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;Count 1&#x27;</span><span style="color:var(--shiki-foreground)">))</span><span style="color:var(--shiki-token-function)">.toBeOnTheScreen</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">});</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>That way we can wrap <code>jest.runAllTimers()</code> call which triggers the <code>setTimeout</code> updates inside an <code>act</code> call, hence resolving the act warning. Note that this whole code is synchronous thanks to usage of Jest fake timers.</p>
<h3 class="rp-toc-include" id="solution-with-real-timers"><a href="#solution-with-real-timers" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Solution with real timers</h3>
<p>If we wanted to stick with real timers then things get a bit more complex. Let’s start by applying a crude solution of opening async <code>act()</code> call for the expected duration of components updates:</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-function)">test</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;render with real timers - sleep&#x27;</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-token-keyword)"> async</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> render</span><span style="color:var(--shiki-foreground)">(&lt;</span><span style="color:var(--shiki-token-constant)">TestAsyncComponent</span><span style="color:var(--shiki-foreground)"> /&gt;);</span></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> await</span><span style="color:var(--shiki-token-function)"> act</span><span style="color:var(--shiki-foreground)">(() </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-token-function)"> sleep</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">100</span><span style="color:var(--shiki-foreground)">)); </span><span style="color:var(--shiki-token-comment)">// Wait a bit longer than setTimeout in `TestAsyncComponent`</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-function)"> expect</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">screen</span><span style="color:var(--shiki-token-function)">.getByText</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;Count 1&#x27;</span><span style="color:var(--shiki-foreground)">))</span><span style="color:var(--shiki-token-function)">.toBeOnTheScreen</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">});</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>This works correctly as we use an explicit async <code>act()</code> call that resolves the console error. However, it relies on our knowledge of exact implementation details which is a bad practice.</p>
<p>Let’s try more elegant solution using <code>waitFor</code> that will wait for our desired state:</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-function)">test</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;render with real timers - waitFor&#x27;</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-token-keyword)"> async</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> render</span><span style="color:var(--shiki-foreground)">(&lt;</span><span style="color:var(--shiki-token-constant)">TestAsyncComponent</span><span style="color:var(--shiki-foreground)"> /&gt;);</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-keyword)"> await</span><span style="color:var(--shiki-token-function)"> waitFor</span><span style="color:var(--shiki-foreground)">(() </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-token-constant)"> screen</span><span style="color:var(--shiki-token-function)">.getByText</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;Count 1&#x27;</span><span style="color:var(--shiki-foreground)">));</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> expect</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-constant)">screen</span><span style="color:var(--shiki-token-function)">.getByText</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;Count 1&#x27;</span><span style="color:var(--shiki-foreground)">))</span><span style="color:var(--shiki-token-function)">.toBeOnTheScreen</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">});</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>This also works correctly, because <code>waitFor</code> call executes async <code>act()</code> call internally.</p>
<p>The above code can be simplified using <code>findBy</code> query:</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-token-function)">test</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;render with real timers - findBy&#x27;</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-token-keyword)"> async</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-foreground)"> {</span></span>
<span class="line"><span style="color:var(--shiki-token-function)"> render</span><span style="color:var(--shiki-foreground)">(&lt;</span><span style="color:var(--shiki-token-constant)">TestAsyncComponent</span><span style="color:var(--shiki-foreground)"> /&gt;);</span></span>
<span class="line"></span>
<span class="line"><span style="color:var(--shiki-token-function)"> expect</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-keyword)">await</span><span style="color:var(--shiki-token-constant)"> screen</span><span style="color:var(--shiki-token-function)">.findByText</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-string-expression)">&#x27;Count 1&#x27;</span><span style="color:var(--shiki-foreground)">))</span><span style="color:var(--shiki-token-function)">.toBeOnTheScreen</span><span style="color:var(--shiki-foreground)">();</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">});</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>This also works since <code>findByText</code> internally calls <code>waitFor</code> which uses async <code>act()</code>.</p>
<p>Note that all of the above examples are async tests using &amp; awaiting async <code>act()</code> function call.</p>
<h3 class="rp-toc-include" id="async-act-warning"><a href="#async-act-warning" class="rp-header-anchor rp-link" aria-hidden="true">#</a>Async act warning</h3>
<p>If we modify any of the above async tests and remove <code>await</code> keyword, then we will trigger the notorious async <code>act()</code>warning:</p>
<div class="rp-codeblock language-jsx"><div class="rp-codeblock__content"><div class="rp-codeblock__content__scroll-container rp-scrollbar rp-scrollbar--always"><pre class="shiki css-variables" style="background-color:var(--shiki-background);color:var(--shiki-foreground)" tabindex="0" data-lang="jsx"><code><span class="line"><span style="color:var(--shiki-foreground)">Warning</span><span style="color:var(--shiki-token-punctuation)">:</span><span style="color:var(--shiki-foreground)"> You called </span><span style="color:var(--shiki-token-function)">act</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-keyword)">async</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-token-keyword)"> ...</span><span style="color:var(--shiki-foreground)">) without </span><span style="color:var(--shiki-token-constant)">await</span><span style="color:var(--shiki-foreground)">. This could lead to unexpected</span></span>
<span class="line"><span style="color:var(--shiki-foreground)">testing behaviour</span><span style="color:var(--shiki-token-punctuation)">,</span><span style="color:var(--shiki-foreground)"> interleaving multiple act calls and mixing their </span><span style="color:var(--shiki-token-constant)">scopes</span><span style="color:var(--shiki-foreground)">. You should</span></span>
<span class="line"><span style="color:var(--shiki-token-keyword)">-</span><span style="color:var(--shiki-token-keyword)"> await</span><span style="color:var(--shiki-token-function)"> act</span><span style="color:var(--shiki-foreground)">(</span><span style="color:var(--shiki-token-keyword)">async</span><span style="color:var(--shiki-foreground)"> () </span><span style="color:var(--shiki-token-keyword)">=&gt;</span><span style="color:var(--shiki-token-keyword)"> ...</span><span style="color:var(--shiki-foreground)">);</span></span></code></pre></div><div class="rp-code-button-group"><button class="rp-code-button-group__button rp-code-wrap-button" title="Toggle code wrap"><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrapped"><path fill="currentColor" d="M21 5H3v2h18zM3 19h7v-2H3zm0-6h15c1 0 2 .43 2 2s-1 2-2 2h-2v-2l-4 3 4 3v-2h2c2.95 0 4-1.27 4-4 0-2.72-1-4-4-4H3z"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="32" height="32" viewBox="0 0 24 24" class="rp-code-button-group__icon rp-code-button-group__icon--wrap"><path fill="currentColor" d="M16 7H3V5h13zM3 19h13v-2H3zm19-7-4-3v2H3v2h15v2z"></path></svg></button><button class="rp-code-button-group__button rp-code-copy-button" title="Copy code"><svg xmlns="http://www.w3.org/2000/svg" width="272" height="272" viewBox="0 0 272 272" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--copy"><path fill="currentColor" fill-rule="evenodd" d="M45.883 23.368h123.823v22.514H68.396v146.336H45.883zm45.026 45.027H225.99v180.107H90.91zm22.514 22.513v135.08h90.053V90.908z" clip-rule="evenodd"></path></svg><svg xmlns="http://www.w3.org/2000/svg" width="271" height="271" viewBox="0 0 271 271" class="rp-code-button-group__icon rp-code-copy-button__icon rp-code-copy-button__icon--success"><path fill="currentColor" d="M112.687 203.223H90.174v-22.514h22.512v-22.514h22.512v22.514h-22.511zm-22.514-22.514H67.66v-22.514h22.513zm-22.514-22.514H45.146v-22.512H67.66zm90.054 0h-22.514v-22.512h22.514zm22.514-22.512h-22.514v-22.514h22.514zm22.513-22.514h-22.513V90.655h22.513zm22.514-22.514H202.74V68.143h22.514z"></path></svg></button></div></div></div>
<p>React decides to show this error whenever it detects that async <code>act()</code>call <a href="https://github.com/facebook/react/blob/ce13860281f833de8a3296b7a3dad9caced102e9/packages/react/src/ReactAct.js#L93" target="_blank" rel="noopener noreferrer" class="rp-link">has not been awaited</a>.</p>
<p>The exact reasons why you might see async <code>act()</code> warnings vary, but finally it means that <code>act()</code> has been called with callback that returns <code>Promise</code>-like object, but it has not been waited on.</p>
<h2 class="rp-toc-include" id="references"><a href="#references" class="rp-header-anchor rp-link" aria-hidden="true">#</a>References</h2>
<ul>
<li><a href="https://github.com/facebook/react/blob/main/packages/react/src/ReactAct.js" target="_blank" rel="noopener noreferrer" class="rp-link">React <code>act</code> implementation source</a></li>
<li><a href="https://reactjs.org/docs/testing-recipes.html#act" target="_blank" rel="noopener noreferrer" class="rp-link">React testing recipes: <code>act()</code></a></li>
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stroke="var(--rp-c-divider-light)" stroke-width="2"></circle><circle cx="7" cy="7" r="6" stroke-linecap="round" fill="none" stroke="var(--rp-c-brand)" stroke-width="2" stroke-dasharray="37.69911184307752" stroke-dashoffset="37.69911184307752" transform="rotate(-90 7 7)" style="transition:stroke-dashoffset 0.3s"></circle></svg></div><nav class="rp-outline__toc rp-scrollbar"><a href="#act-warnings" class="rp-toc-item rp-link" title="act warnings" style="padding-left:0" data-depth="0"><span class="rp-toc-item__text rp-doc"><code>act</code> warnings</span></a><a href="#synchronous-act" class="rp-toc-item rp-link" title="Synchronous act" style="padding-left:0" data-depth="0"><span class="rp-toc-item__text rp-doc">Synchronous <code>act</code></span></a><a href="#responsibility" class="rp-toc-item rp-link" title="Responsibility" style="padding-left:12px" data-depth="1"><span class="rp-toc-item__text rp-doc">Responsibility</span></a><a href="#when-to-use-act" class="rp-toc-item rp-link" title="When to use act" style="padding-left:12px" data-depth="1"><span class="rp-toc-item__text rp-doc">When to use act</span></a><a href="#implementation" class="rp-toc-item rp-link" title="Implementation" style="padding-left:12px" data-depth="1"><span class="rp-toc-item__text rp-doc">Implementation</span></a><a href="#asynchronous-act" class="rp-toc-item rp-link" title="Asynchronous act" style="padding-left:0" data-depth="0"><span class="rp-toc-item__text rp-doc">Asynchronous <code>act</code></span></a><a href="#asynchronous-code" class="rp-toc-item rp-link" title="Asynchronous code" style="padding-left:12px" data-depth="1"><span class="rp-toc-item__text rp-doc">Asynchronous code</span></a><a href="#solution-with-fake-timers" class="rp-toc-item rp-link" title="Solution with fake timers" style="padding-left:12px" data-depth="1"><span class="rp-toc-item__text rp-doc">Solution with fake timers</span></a><a href="#solution-with-real-timers" class="rp-toc-item rp-link" title="Solution 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