mirror of
https://github.com/callstack/react-native-testing-library.git
synced 2026-09-18 23:09:04 +08:00
github-actions[bot]
16 lines
93 KiB
HTML
16 lines
93 KiB
HTML
<!doctype html>
|
||
<html lang="en" dir="ltr" class="docs-wrapper docs-doc-page docs-version-current plugin-docs plugin-id-default docs-doc-id-understanding-act">
|
||
<head>
|
||
<meta charset="UTF-8">
|
||
<meta name="generator" content="Docusaurus v2.3.1">
|
||
<title data-rh="true">Understanding Act function | React Native Testing Library</title><meta data-rh="true" name="viewport" content="width=device-width,initial-scale=1"><meta data-rh="true" name="twitter:card" content="summary_large_image"><meta data-rh="true" property="og:image" content="https://callstack.github.io/react-native-testing-library/img/owl.png"><meta data-rh="true" name="twitter:image" content="https://callstack.github.io/react-native-testing-library/img/owl.png"><meta data-rh="true" property="og:url" content="https://callstack.github.io/react-native-testing-library/docs/understanding-act"><meta data-rh="true" name="docusaurus_locale" content="en"><meta data-rh="true" name="docsearch:language" content="en"><meta data-rh="true" name="docusaurus_version" content="current"><meta data-rh="true" name="docusaurus_tag" content="docs-default-current"><meta data-rh="true" name="docsearch:version" content="current"><meta data-rh="true" name="docsearch:docusaurus_tag" content="docs-default-current"><meta data-rh="true" property="og:title" content="Understanding Act function | React Native Testing Library"><meta data-rh="true" 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."><meta data-rh="true" 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."><link data-rh="true" rel="icon" href="/react-native-testing-library/img/owl.png"><link data-rh="true" rel="canonical" href="https://callstack.github.io/react-native-testing-library/docs/understanding-act"><link data-rh="true" rel="alternate" href="https://callstack.github.io/react-native-testing-library/docs/understanding-act" hreflang="en"><link data-rh="true" rel="alternate" href="https://callstack.github.io/react-native-testing-library/docs/understanding-act" hreflang="x-default"><link data-rh="true" rel="preconnect" href="https://6CJ0BV6AVN-dsn.algolia.net" crossorigin="anonymous"><link rel="search" type="application/opensearchdescription+xml" title="React Native Testing Library" href="/react-native-testing-library/opensearch.xml"><link rel="stylesheet" href="/react-native-testing-library/assets/css/styles.24db0bc4.css">
|
||
<link rel="preload" href="/react-native-testing-library/assets/js/runtime~main.77ca6133.js" as="script">
|
||
<link rel="preload" href="/react-native-testing-library/assets/js/main.fd9ae3b5.js" as="script">
|
||
</head>
|
||
<body class="navigation-with-keyboard">
|
||
<script>!function(){function t(t){document.documentElement.setAttribute("data-theme",t)}var e=function(){var t=null;try{t=localStorage.getItem("theme")}catch(t){}return t}();t(null!==e?e:"light")}()</script><div id="__docusaurus">
|
||
<div role="region" aria-label="Skip to main content"><a class="skipToContent_fXgn" href="#docusaurus_skipToContent_fallback">Skip to main content</a></div><nav aria-label="Main" class="navbar navbar--fixed-top"><div class="navbar__inner"><div class="navbar__items"><button aria-label="Toggle navigation bar" aria-expanded="false" class="navbar__toggle clean-btn" type="button"><svg width="30" height="30" viewBox="0 0 30 30" aria-hidden="true"><path stroke="currentColor" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2" d="M4 7h22M4 15h22M4 23h22"></path></svg></button><a class="navbar__brand" href="/react-native-testing-library/"><div class="navbar__logo"><img src="/react-native-testing-library/img/owl.png" alt="React Native Testing Library" class="themedImage_ToTc themedImage--light_HNdA"><img src="/react-native-testing-library/img/owl.png" alt="React Native Testing Library" class="themedImage_ToTc themedImage--dark_i4oU"></div><b class="navbar__title text--truncate">React Native Testing Library</b></a></div><div class="navbar__items navbar__items--right"><a class="navbar__item navbar__link" href="/react-native-testing-library/docs/getting-started">Docs</a><a href="https://github.com/callstack/react-native-testing-library" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link">GitHub<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a><div class="toggle_vylO colorModeToggle_DEke"><button class="clean-btn toggleButton_gllP toggleButtonDisabled_aARS" type="button" disabled="" title="Switch between dark and light mode (currently light mode)" aria-label="Switch between dark and light mode (currently light mode)" aria-live="polite"><svg viewBox="0 0 24 24" width="24" height="24" class="lightToggleIcon_pyhR"><path fill="currentColor" d="M12,9c1.65,0,3,1.35,3,3s-1.35,3-3,3s-3-1.35-3-3S10.35,9,12,9 M12,7c-2.76,0-5,2.24-5,5s2.24,5,5,5s5-2.24,5-5 S14.76,7,12,7L12,7z M2,13l2,0c0.55,0,1-0.45,1-1s-0.45-1-1-1l-2,0c-0.55,0-1,0.45-1,1S1.45,13,2,13z M20,13l2,0c0.55,0,1-0.45,1-1 s-0.45-1-1-1l-2,0c-0.55,0-1,0.45-1,1S19.45,13,20,13z M11,2v2c0,0.55,0.45,1,1,1s1-0.45,1-1V2c0-0.55-0.45-1-1-1S11,1.45,11,2z M11,20v2c0,0.55,0.45,1,1,1s1-0.45,1-1v-2c0-0.55-0.45-1-1-1C11.45,19,11,19.45,11,20z M5.99,4.58c-0.39-0.39-1.03-0.39-1.41,0 c-0.39,0.39-0.39,1.03,0,1.41l1.06,1.06c0.39,0.39,1.03,0.39,1.41,0s0.39-1.03,0-1.41L5.99,4.58z M18.36,16.95 c-0.39-0.39-1.03-0.39-1.41,0c-0.39,0.39-0.39,1.03,0,1.41l1.06,1.06c0.39,0.39,1.03,0.39,1.41,0c0.39-0.39,0.39-1.03,0-1.41 L18.36,16.95z M19.42,5.99c0.39-0.39,0.39-1.03,0-1.41c-0.39-0.39-1.03-0.39-1.41,0l-1.06,1.06c-0.39,0.39-0.39,1.03,0,1.41 s1.03,0.39,1.41,0L19.42,5.99z M7.05,18.36c0.39-0.39,0.39-1.03,0-1.41c-0.39-0.39-1.03-0.39-1.41,0l-1.06,1.06 c-0.39,0.39-0.39,1.03,0,1.41s1.03,0.39,1.41,0L7.05,18.36z"></path></svg><svg viewBox="0 0 24 24" width="24" height="24" class="darkToggleIcon_wfgR"><path fill="currentColor" d="M9.37,5.51C9.19,6.15,9.1,6.82,9.1,7.5c0,4.08,3.32,7.4,7.4,7.4c0.68,0,1.35-0.09,1.99-0.27C17.45,17.19,14.93,19,12,19 c-3.86,0-7-3.14-7-7C5,9.07,6.81,6.55,9.37,5.51z M12,3c-4.97,0-9,4.03-9,9s4.03,9,9,9s9-4.03,9-9c0-0.46-0.04-0.92-0.1-1.36 c-0.98,1.37-2.58,2.26-4.4,2.26c-2.98,0-5.4-2.42-5.4-5.4c0-1.81,0.89-3.42,2.26-4.4C12.92,3.04,12.46,3,12,3L12,3z"></path></svg></button></div><div class="searchBox_ZlJk"><button type="button" class="DocSearch DocSearch-Button" aria-label="Search"><span class="DocSearch-Button-Container"><svg width="20" height="20" class="DocSearch-Search-Icon" viewBox="0 0 20 20"><path d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z" stroke="currentColor" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"></path></svg><span class="DocSearch-Button-Placeholder">Search</span></span><span class="DocSearch-Button-Keys"></span></button></div></div></div><div role="presentation" class="navbar-sidebar__backdrop"></div></nav><div id="docusaurus_skipToContent_fallback" class="main-wrapper mainWrapper_z2l0 docsWrapper_BCFX"><button aria-label="Scroll back to top" class="clean-btn theme-back-to-top-button backToTopButton_sjWU" type="button"></button><div class="docPage__5DB"><aside class="theme-doc-sidebar-container docSidebarContainer_b6E3"><div class="sidebarViewport_Xe31"><div class="sidebar_njMd"><nav aria-label="Docs sidebar" class="menu thin-scrollbar menu_SIkG"><ul class="theme-doc-sidebar-menu menu__list"><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link">Introduction</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/getting-started">Getting Started</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/faq">FAQ</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link">API Reference</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/api">API</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/api-queries">Queries</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/jest-matchers">Jest Matchers</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/user-event">User Event</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link">Guides</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/how-should-i-query">How Should I Query?</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/eslint-plugin-testing-library">ESLint Plugin Testing Library Compatibility</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/troubleshooting">Troubleshooting</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--active">Advanced</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/testing-env">Testing Environment</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="/react-native-testing-library/docs/understanding-act">Understanding Act function</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link">Migrations</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/migration-jest-native">Migration from Jest Native matchers</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/migration-v12">Migration to 12.0</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/migration-v11">Migration to 11.0</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/migration-v9">Migration to 9.0</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/migration-v7">Migration to 7.0</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/migration-v2">Migration to 2.0</a></li></ul></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link">Examples</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/react-navigation">React Navigation</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/react-native-testing-library/docs/redux-integration">Redux Integration</a></li></ul></li></ul></nav></div></div></aside><main class="docMainContainer_gTbr"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_VOVn"><div class="docItemContainer_Djhp"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label="Breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a aria-label="Home page" class="breadcrumbs__link" href="/react-native-testing-library/"><svg viewBox="0 0 24 24" class="breadcrumbHomeIcon_YNFT"><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Advanced</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Understanding Act function</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Understanding Act function</h1></header><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"><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><div class="tableOfContentsInline_prmo"><ul class="table-of-contents"><li><a href="#act-warnings"><code>act</code> warnings</a></li><li><a href="#synchronous-act">Synchronous <code>act</code></a><ul><li><a href="#responsibility">Responsibility</a></li><li><a href="#when-to-use-act">When to use act</a></li><li><a href="#implementation">Implementation</a></li></ul></li><li><a href="#asynchronous-act">Asynchronous <code>act</code></a><ul><li><a href="#asynchronous-code">Asynchronous code</a></li><li><a href="#solution-with-fake-timers">Solution with fake timers</a></li><li><a href="#solution-with-real-timers">Solution with real timers</a></li><li><a href="#async-act-warning">Async act warning</a></li></ul></li><li><a href="#references">References</a></li></ul></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="act-warnings"><code>act</code> warnings<a href="#act-warnings" class="hash-link" aria-label="Direct link to act-warnings" title="Direct link to act-warnings"></a></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 "sync <code>act()</code>" warning:</p><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token literal-property property" style="color:#36acaa">Warning</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">An</span><span class="token plain"> update to </span><span class="token maybe-class-name">Component</span><span class="token plain"> inside a test was not wrapped </span><span class="token keyword" style="color:#00009f">in</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token property-access maybe-class-name">When</span><span class="token plain"> testing</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> code that causes </span><span class="token maybe-class-name">React</span><span class="token plain"> state updates should be wrapped into </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/* fire events that update state */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">/* assert on the output */</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>The second one relates to async usage of <code>act</code> so let’s call it the "async <code>act</code>" error:</p><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token literal-property property" style="color:#36acaa">Warning</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">You</span><span class="token plain"> called </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">async</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> without </span><span class="token keyword control-flow" style="color:#00009f">await</span><span class="token punctuation" style="color:#393A34">.</span><span class="token plain"> </span><span class="token property-access maybe-class-name">This</span><span class="token plain"> could lead to unexpected</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">testing behaviour</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> interleaving multiple act calls and mixing their scopes</span><span class="token punctuation" style="color:#393A34">.</span><span class="token plain"> </span><span class="token property-access maybe-class-name">You</span><span class="token plain"> should</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token operator" style="color:#393A34">-</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">await</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">async</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="synchronous-act">Synchronous <code>act</code><a href="#synchronous-act" class="hash-link" aria-label="Direct link to synchronous-act" title="Direct link to synchronous-act"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="responsibility">Responsibility<a href="#responsibility" class="hash-link" aria-label="Direct link to Responsibility" title="Direct link to Responsibility"></a></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function maybe-class-name" style="color:#d73a49">TestComponent</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">count</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> setCount</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token maybe-class-name">React</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">useState</span><span class="token punctuation" style="color:#393A34">(</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token maybe-class-name">React</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">useEffect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">setCount</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">c</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> c </span><span class="token operator" style="color:#393A34">+</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> </span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">Text</span><span class="token tag punctuation" style="color:#393A34">></span><span class="token plain-text">Count </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain">count</span><span class="token punctuation" style="color:#393A34">}</span><span class="token tag punctuation" style="color:#393A34"></</span><span class="token tag class-name" style="color:#00009f">Text</span><span class="token tag punctuation" style="color:#393A34">></span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token function" style="color:#d73a49">test</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'render without act'</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> renderer </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token maybe-class-name">TestRenderer</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">create</span><span class="token punctuation" style="color:#393A34">(</span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">TestComponent</span><span class="token tag" style="color:#00009f"> </span><span class="token tag punctuation" style="color:#393A34">/></span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// Bind RNTL queries for root element.</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> view </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">within</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">renderer</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">view</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">getByText</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'Count 0'</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">toBeOnTheScreen</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token function" style="color:#d73a49">test</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'render with act'</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">let</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">renderer</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">ReactTestRenderer</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> renderer </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token maybe-class-name">TestRenderer</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">create</span><span class="token punctuation" style="color:#393A34">(</span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">TestComponent</span><span class="token tag" style="color:#00009f"> </span><span class="token tag punctuation" style="color:#393A34">/></span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// Bind RNTL queries for root element.</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> view </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">within</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">renderer</span><span class="token operator" style="color:#393A34">!</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">root</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">view</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">getByText</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'Count 1'</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">toBeOnTheScreen</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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="anchor anchorWithStickyNavbar_LWe7" id="when-to-use-act">When to use act<a href="#when-to-use-act" class="hash-link" aria-label="Direct link to When to use act" title="Direct link to When to use act"></a></h3><p>The name <code>act</code> comes from <a href="http://wiki.c2.com/?ArrangeActAssert" target="_blank" rel="noopener noreferrer">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">are not supported</a>.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="implementation">Implementation<a href="#implementation" class="hash-link" aria-label="Direct link to Implementation" title="Direct link to Implementation"></a></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">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">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">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="anchor anchorWithStickyNavbar_LWe7" id="asynchronous-act">Asynchronous <code>act</code><a href="#asynchronous-act" class="hash-link" aria-label="Direct link to asynchronous-act" title="Direct link to asynchronous-act"></a></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">object resembling promise</a>.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="asynchronous-code">Asynchronous code<a href="#asynchronous-code" class="hash-link" aria-label="Direct link to Asynchronous code" title="Direct link to Asynchronous code"></a></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function maybe-class-name" style="color:#d73a49">TestAsyncComponent</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">count</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> setCount</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token maybe-class-name">React</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">useState</span><span class="token punctuation" style="color:#393A34">(</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token maybe-class-name">React</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">useEffect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">setTimeout</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">setCount</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">c</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> c </span><span class="token operator" style="color:#393A34">+</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">50</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> </span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">Text</span><span class="token tag punctuation" style="color:#393A34">></span><span class="token plain-text">Count </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain">count</span><span class="token punctuation" style="color:#393A34">}</span><span class="token tag punctuation" style="color:#393A34"></</span><span class="token tag class-name" style="color:#00009f">Text</span><span class="token tag punctuation" style="color:#393A34">></span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token function" style="color:#d73a49">test</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'render async natively'</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> view </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">render</span><span class="token punctuation" style="color:#393A34">(</span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">TestAsyncComponent</span><span class="token tag" style="color:#00009f"> </span><span class="token tag punctuation" style="color:#393A34">/></span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">view</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">getByText</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'Count 0'</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">toBeOnTheScreen</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token literal-property property" style="color:#36acaa">Warning</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">An</span><span class="token plain"> update to </span><span class="token maybe-class-name">TestAsyncComponent</span><span class="token plain"> inside a test was not wrapped </span><span class="token keyword" style="color:#00009f">in</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token property-access maybe-class-name">When</span><span class="token plain"> testing</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> code that causes </span><span class="token maybe-class-name">React</span><span class="token plain"> state updates should be wrapped into </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/* fire events that update state */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">/* assert on the output */</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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="anchor anchorWithStickyNavbar_LWe7" id="solution-with-fake-timers">Solution with fake timers<a href="#solution-with-fake-timers" class="hash-link" aria-label="Direct link to Solution with fake timers" title="Direct link to Solution with fake timers"></a></h3><p>First solution is to use Jest's fake timers inside out tests:</p><div class="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token function" style="color:#d73a49">test</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'render with fake timers'</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> jest</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">useFakeTimers</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> view </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">render</span><span class="token punctuation" style="color:#393A34">(</span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">TestAsyncComponent</span><span class="token tag" style="color:#00009f"> </span><span class="token tag punctuation" style="color:#393A34">/></span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> jest</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">runAllTimers</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">view</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">getByText</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'Count 1'</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">toBeOnTheScreen</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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="anchor anchorWithStickyNavbar_LWe7" id="solution-with-real-timers">Solution with real timers<a href="#solution-with-real-timers" class="hash-link" aria-label="Direct link to Solution with real timers" title="Direct link to Solution with real timers"></a></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token function" style="color:#d73a49">test</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'render with real timers - sleep'</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">async</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> view </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">render</span><span class="token punctuation" style="color:#393A34">(</span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">TestAsyncComponent</span><span class="token tag" style="color:#00009f"> </span><span class="token tag punctuation" style="color:#393A34">/></span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">await</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">async</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">await</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">sleep</span><span class="token punctuation" style="color:#393A34">(</span><span class="token number" style="color:#36acaa">100</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// Wait a bit longer than setTimeout in `TestAsyncComponent`</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">view</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">getByText</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'Count 1'</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">toBeOnTheScreen</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token function" style="color:#d73a49">test</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'render with real timers - waitFor'</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">async</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> view </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">render</span><span class="token punctuation" style="color:#393A34">(</span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">TestAsyncComponent</span><span class="token tag" style="color:#00009f"> </span><span class="token tag punctuation" style="color:#393A34">/></span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">await</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">waitFor</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> view</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">getByText</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'Count 1'</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">view</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">getByText</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'Count 1'</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">toBeOnTheScreen</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token function" style="color:#d73a49">test</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'render with real timers - findBy'</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">async</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> view </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">render</span><span class="token punctuation" style="color:#393A34">(</span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">TestAsyncComponent</span><span class="token tag" style="color:#00009f"> </span><span class="token tag punctuation" style="color:#393A34">/></span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword control-flow" style="color:#00009f">await</span><span class="token plain"> view</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">findByText</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">'Count 1'</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">toBeOnTheScreen</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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 & awaiting async <code>act()</code> function call.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="async-act-warning">Async act warning<a href="#async-act-warning" class="hash-link" aria-label="Direct link to Async act warning" title="Direct link to Async act warning"></a></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="language-jsx codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-jsx codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token literal-property property" style="color:#36acaa">Warning</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">You</span><span class="token plain"> called </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">async</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> without </span><span class="token keyword control-flow" style="color:#00009f">await</span><span class="token punctuation" style="color:#393A34">.</span><span class="token plain"> </span><span class="token property-access maybe-class-name">This</span><span class="token plain"> could lead to unexpected</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">testing behaviour</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> interleaving multiple act calls and mixing their scopes</span><span class="token punctuation" style="color:#393A34">.</span><span class="token plain"> </span><span class="token property-access maybe-class-name">You</span><span class="token plain"> should</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token operator" style="color:#393A34">-</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">await</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">act</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">async</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token spread operator" style="color:#393A34">...</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></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">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="anchor anchorWithStickyNavbar_LWe7" id="references">References<a href="#references" class="hash-link" aria-label="Direct link to References" title="Direct link to References"></a></h2><ul><li><a href="https://github.com/facebook/react/blob/main/packages/react/src/ReactAct.js" target="_blank" rel="noopener noreferrer">React <code>act</code> implementation source</a></li><li><a href="https://reactjs.org/docs/testing-recipes.html#act" target="_blank" rel="noopener noreferrer">React testing recipes: <code>act()</code></a></li></ul></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/callstack/react-native-testing-library/blob/main/website/docs/UnderstandingAct.md" target="_blank" rel="noreferrer noopener" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col lastUpdated_vwxv"></div></div></footer></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><a class="pagination-nav__link pagination-nav__link--prev" href="/react-native-testing-library/docs/testing-env"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Testing Environment</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/react-native-testing-library/docs/migration-jest-native"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">Migration from Jest Native matchers</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#act-warnings" class="table-of-contents__link toc-highlight"><code>act</code> warnings</a></li><li><a href="#synchronous-act" class="table-of-contents__link toc-highlight">Synchronous <code>act</code></a><ul><li><a href="#responsibility" class="table-of-contents__link toc-highlight">Responsibility</a></li><li><a href="#when-to-use-act" class="table-of-contents__link toc-highlight">When to use act</a></li><li><a href="#implementation" class="table-of-contents__link toc-highlight">Implementation</a></li></ul></li><li><a href="#asynchronous-act" class="table-of-contents__link toc-highlight">Asynchronous <code>act</code></a><ul><li><a href="#asynchronous-code" class="table-of-contents__link toc-highlight">Asynchronous code</a></li><li><a href="#solution-with-fake-timers" class="table-of-contents__link toc-highlight">Solution with fake timers</a></li><li><a href="#solution-with-real-timers" class="table-of-contents__link toc-highlight">Solution with real timers</a></li><li><a href="#async-act-warning" class="table-of-contents__link toc-highlight">Async act warning</a></li></ul></li><li><a href="#references" class="table-of-contents__link toc-highlight">References</a></li></ul></div></div></div></div></main></div></div><footer class="footer footer--dark"><div class="container container-fluid"><div class="row footer__links"><div class="col footer__col"><div class="footer__title">Docs</div><ul class="footer__items clean-list"><li class="footer__item"><a class="footer__link-item" href="/react-native-testing-library/docs/getting-started">Getting started</a></li><li class="footer__item"><a class="footer__link-item" href="/react-native-testing-library/docs/api">API</a></li></ul></div><div class="col footer__col"><div class="footer__title">Community</div><ul class="footer__items clean-list"><li class="footer__item"><a href="http://stackoverflow.com/questions/tagged/react-native-testing-library" target="_blank" rel="noopener noreferrer" class="footer__link-item">Stack Overflow<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li class="footer__item"><a href="https://discord.gg/QbGezWe" target="_blank" rel="noopener noreferrer" class="footer__link-item">Discord Channel<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li></ul></div><div class="col footer__col"><div class="footer__title">More</div><ul class="footer__items clean-list"><li class="footer__item"><a href="https://github.com/callstack/react-native-testing-library" target="_blank" rel="noopener noreferrer" class="footer__link-item">GitHub<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li><li class="footer__item"><a href="https://github.com/callstack/react-native-testing-library" target="_blank" rel="noopener noreferrer" class="footer__link-item">Star<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_nPIU"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></a></li></ul></div></div><div class="footer__bottom text--center"><div class="footer__copyright">Copyright © 2024 Callstack Open Source</div></div></div></footer></div>
|
||
<script src="/react-native-testing-library/assets/js/runtime~main.77ca6133.js"></script>
|
||
<script src="/react-native-testing-library/assets/js/main.fd9ae3b5.js"></script>
|
||
</body>
|
||
</html> |