build: Cypress React 18 support and React version switcher

cypress/support/index.d.ts

@@ -1,6 +1,7 @@
-import { mount } from 'cypress/react';
 import { ContextObject, Result, RunOptions } from 'axe-core';
 import { realPress } from 'cypress-real-events/commands/realPress';
+import type { mountCommand } from './setup/mount';
+import type { realMountCommand } from './setup/realMount';
 
 type KeyOrShortcut = Parameters<typeof realPress>[0];
 type RealPressOptions = Parameters<typeof realPress>[1];
@@ -30,13 +31,13 @@ declare global {
       /**
        * Mounts components with a basic `EuiProvider` wrapper
        */
-      mount: typeof mount;
+      mount: mountCommand;
 
       /**
        * This ensures the correct testing window has focus when using Cypress Real Events.
        * @see https://github.com/dmtrKovalenko/cypress-real-events/issues/196
        */
-      realMount: typeof mount;
+      realMount: realMountCommand;
 
       /**
        * Repeat the Real Events `realPress()` method 2 or more times

cypress/support/setup/mount.tsx

@@ -0,0 +1,30 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+import React, { ReactNode } from 'react';
+import { EuiProvider } from '../../../src';
+import type { mount } from '@cypress/react18';
+
+// Pick cypress mount function based on which React version is currently being
+// tested. It has to be directly compared against process.env.REACT_VERSION
+// for tree-shaking to work and not throw an error because of a missing import.
+let cypressMount: typeof mount;
+if (process.env.REACT_VERSION === '18') {
+  cypressMount = require('@cypress/react18').mount;
+} else {
+  cypressMount = require('@cypress/react').mount;
+}
+
+const mountCommand = (children: ReactNode): ReturnType<typeof mount> => {
+  return cypressMount(<EuiProvider>{children}</EuiProvider>);
+};
+
+// Export only the type to not confuse code-completion tools
+export type mountCommand = typeof mountCommand;
+
+Cypress.Commands.add('mount', mountCommand);

cypress/support/setup/realMount.js → cypress/support/setup/realMount.tsx

@@ -6,21 +6,26 @@
  * Side Public License, v 1.
  */
 
-import { React, Fragment } from 'react';
+import React, { ReactNode } from 'react';
 import './mount';
 
-Cypress.Commands.add('realMount', (children) => {
+const realMountCommand = (children: ReactNode) => {
   cy.mount(
-    <Fragment>
+    <>
       <div
         data-test-subj="cypress-real-event-target"
         style={{ height: '1px', width: '1px' }}
       />
       {children}
-    </Fragment>
+    </>
   ).then(() => {
     cy.get('[data-test-subj="cypress-real-event-target"]').realClick({
       position: 'topLeft',
     });
   });
-});
+};
+
+// Export only the type to not confuse code-completion tools
+export type realMountCommand = typeof realMountCommand;
+
+Cypress.Commands.add('realMount', realMountCommand);

cypress/webpack.config.js

@@ -12,6 +12,15 @@ const { ProvidePlugin, DefinePlugin } = require('webpack');
 
 const THEME_IMPORT = `'../../dist/eui_theme_${process.env.THEME}.css'`;
 
+const alias = {};
+const reactVersion = process.env.REACT_VERSION || '18';
+
+// Setup module aliasing when we're testing an older React version
+if (['16', '17'].includes(reactVersion)) {
+  alias.react = `react-${reactVersion}`;
+  alias['react-dom'] = `react-dom-${reactVersion}`;
+}
+
 module.exports = {
   mode: 'development',
 
@@ -26,6 +35,7 @@ module.exports = {
       os: false,
       process: require.resolve('process/browser'),
     },
+    alias,
   },
 
   module: {
@@ -46,9 +56,9 @@ module.exports = {
             loader: 'style-loader',
             options: {
               insert: 'meta[name="css-styles"]',
-            }
+            },
           },
-          'css-loader'
+          'css-loader',
         ],
         exclude: /node_modules/,
       },
@@ -62,7 +72,8 @@ module.exports = {
     }),
 
     new DefinePlugin({
-      THEME_IMPORT, // allow cypress/suport/index.js to require the correct css file
+      THEME_IMPORT, // allow cypress/support/component.tsx to require the correct css file
+      'process.env.REACT_VERSION': JSON.stringify(reactVersion),
     }),
   ],
 };

package.json

@@ -117,7 +117,8 @@
     "@babel/preset-typescript": "^7.21.5",
     "@babel/template": "^7.21.9",
     "@cypress/code-coverage": "^3.10.0",
-    "@cypress/react": "^5.10.3",
+    "@cypress/react": "^7.0.3",
+    "@cypress/react18": "^2.0.0",
     "@cypress/webpack-dev-server": "^1.7.0",
     "@elastic/charts": "^53.1.1",
     "@elastic/datemath": "^5.0.3",
@@ -226,8 +227,12 @@
     "puppeteer": "^5.5.0",
     "raw-loader": "^4.0.1",
     "react": "^18.2.0",
+    "react-16": "npm:react@^16.14.0",
+    "react-17": "npm:react@^17.0.2",
     "react-docgen-typescript": "^2.2.2",
     "react-dom": "^18.2.0",
+    "react-dom-16": "npm:react-dom@^16.14.0",
+    "react-dom-17": "npm:react-dom@^17.0.2",
     "react-helmet": "^6.1.0",
     "react-redux": "^7.2.1",
     "react-refresh": "^0.11.0",

scripts/cypress.js

@@ -21,16 +21,24 @@ const argv = yargs(hideBin(process.argv))
     dev: { type: 'boolean' },
     theme: { type: 'string', default: 'light', choices: ['light', 'dark'] },
     a11y: { type: 'boolean' },
+    'react-version': {
+      type: 'number',
+      default: 18,
+      choices: [16, 17, 18],
+    },
   }).argv;
 
 const isDev = argv.hasOwnProperty('dev');
 const isA11y = argv.hasOwnProperty('a11y');
 const skipScss = argv.hasOwnProperty('skip-css');
 const theme = argv.theme;
+const reactVersion = argv['react-version'];
 
 const info = chalk.white;
 const log = chalk.grey;
 
+console.log(info(`Running tests on React v${reactVersion}`));
+
 // compile scss -> css so tests can render correctly
 if (!skipScss) {
   console.log(info('Compiling SCSS'));
@@ -54,6 +62,7 @@ const cypressCommandParts = [
   `THEME=${theme}`, // pass the theme
   'BABEL_MODULES=false', // let webpack receive ES Module code
   'NODE_ENV=cypress_test', // enable code coverage checks
+  `REACT_VERSION=${reactVersion}`, // set react version to test
   `cypress ${testParams}`,
   ...argv._, // pass any extra options given to this script
 ];

wiki/contributing-to-eui/testing/cypress-testing.md

@@ -18,6 +18,11 @@ By default tests are run using the light theme. Dark mode can be enabled by pass
 
 To ensure tests use up-to-date styles, the test runner compiles our SCSS to CSS before executing Cypress. This adds some processing time before the tests can run, and often the existing locally-built styles are still accurate. The CSS compilation step can be skipped by passing the `--skip-css` flag to `yarn test-cypress`, `yarn test-cypress-dev` and `yarn test-cypress-a11y`.
 
+### Testing specific version of React
+
+By default, EUI Cypress tests are run using the latest supported version of React.
+You can change that behavior and run e2e tests using a different React version by passing the `--react-version` option set to `16`, `17` or `18`. 
+
 ### Cypress arguments
 
 You can also pass [Cypress CLI arguments](https://docs.cypress.io/guides/guides/command-line). For example: