Mocha organizes JavaScript tests; Selenium WebDriver drives the browser; Node.js assertions verify what the user sees. Install both packages, create a driver in Mocha’s before hook, quit it in after, and run the test with npx mocha. This guide uses CommonJS and a local Chrome browser, then shows how to adapt the setup for remote Selenium servers.
What Mocha and Selenium each do
Mocha is the test runner: its describe and it functions organize suites and test cases, while lifecycle hooks handle setup and cleanup. Selenium WebDriver sends commands to a browser, such as navigating to a page, entering text, and clicking a button. Node.js’s built-in assert module checks whether the observed result matches expectations.
A useful browser test verifies the result of a user flow, not just that a WebDriver command completed. The example below submits Selenium’s demonstration form and checks for its confirmation message.
Install Node.js and the packages
Use a Node.js version that satisfies both documented package requirements: Mocha v12.0.0 requires ^20.19.0 || >=22.12.0, while Selenium’s JavaScript bindings require Node.js >=22. Node.js 22.12 or later is within both stated ranges. Confirm the requirements again when you update either dependency.
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Check your installed Node.js and npm versions:
node --version npm --version -
Create a project directory and initialize it if you do not already have a package file:
mkdir mocha-selenium-example cd mocha-selenium-example npm init -y -
Install Mocha as a development dependency and Selenium WebDriver:
npm install --save-dev mocha npm install selenium-webdriver
Selenium Manager handles browser-driver installation in the basic documented JavaScript flow. You still need a browser installed for a local run. The example selects Chrome; to use another supported browser, change the browser name in the builder and ensure that browser is available in your environment.
Write and run a CommonJS test
Create runningTests.spec.js in the project directory. This example follows Selenium’s documented Mocha pattern and uses CommonJS require imports:
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const { By, Builder } = require('selenium-webdriver');
const assert = require('node:assert/strict');
describe('First script', function () {
let driver;
before(async function () {
driver = await new Builder().forBrowser('chrome').build();
});
after(async function () {
if (driver) await driver.quit();
});
it('submits a form and shows the response', async function () {
await driver.get('https://www.selenium.dev/selenium/web/web-form.html');
await driver.findElement(By.name('my-text')).sendKeys('Selenium');
await driver.findElement(By.css('button')).click();
const message = await driver.findElement(By.id('message')).getText();
assert.equal(message, 'Received!');
});
});Run it from the project directory:
npx mocha runningTests.spec.jsMocha should report one passing test if the browser can start, the demonstration page loads, and the confirmation text matches. The assertions use strict Node.js comparison semantics because the test imports node:assert/strict.
Choose hooks and driver scope
One driver for a suite
The sample creates one driver in before and closes it in after. Those hooks run once for the suite block, so this is a compact choice when tests can share a browser session. The guarded quit() prevents cleanup from trying to close a driver if setup failed before assignment.
A fresh browser for each test
Use beforeEach and afterEach when each test needs independent browser state. This adds startup and teardown for every test, but avoids carrying cookies, navigation state, or other session changes from one test into another.
describe('Independent browser tests', function () {
let driver;
beforeEach(async function () {
driver = await new Builder().forBrowser('chrome').build();
});
afterEach(async function () {
if (driver) await driver.quit();
});
it('opens the form page', async function () {
await driver.get('https://www.selenium.dev/selenium/web/web-form.html');
assert.match(await driver.getTitle(), /Web form/);
});
});Mocha awaits asynchronous tests and hooks, so use async/await for WebDriver operations and cleanup. Keep teardown in a hook rather than only at the end of a test: a failed assertion should not skip browser cleanup.
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Use a remote Selenium server
A local browser and a remote Selenium server are different execution arrangements. Selenium Manager simplifies local browser-driver setup; it does not create or host a remote Grid. For a Grid or standalone Selenium server that is already reachable, point the builder at its server URL:
const driver = await new Builder()
.forBrowser('chrome')
.usingServer('http://localhost:4444')
.build();The Selenium JavaScript API also documents the SELENIUM_REMOTE_URL environment variable for remote configuration. Set it to the accessible server endpoint in the environment that runs the test. Check your server’s address and availability if session creation fails.
Common failures and fixes
-
Mocha or Selenium reports an unsupported Node version: compare
node --versionwith both package requirements. The overlap stated in current documentation is Node.js 22.12 or later. -
The browser cannot be started: confirm the selected browser is installed and can launch in the machine or container running the test. Selenium Manager handles driver installation in the basic JavaScript flow, but does not install the browser itself.
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A remote session cannot be created: confirm that the Selenium server is running and reachable at the configured URL, and that the remote configuration is present in the test process environment.
-
An element lookup fails: verify that navigation completed, the page contains the locator you selected, and the locator matches that page. This demo uses a name, CSS selector, and ID from Selenium’s own sample form; selectors for your application should reflect its actual markup.
-
The test ends but browser processes remain: ensure the driver is assigned during setup and that the suite’s
afteror per-testafterEachhook calls and awaitsdriver.quit().
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Sources and compatibility notes
For current syntax and package requirements, see the Selenium first-script guide, Selenium JavaScript API documentation, Mocha Getting Started, and Mocha Hooks. The JavaScript API page lists Node.js support end dates of 2027-04-30 for Node 22, 2028-04-30 for Node 24, and 2029-04-30 for Node 26; these are support-policy dates shown on that page, not a guarantee about every future Selenium release.
Frequently Asked Questions
Can I use ES modules instead of CommonJS?
Yes. Use one module system consistently with your project configuration and import syntax; Mocha’s current getting-started guide demonstrates ESM, while Selenium’s Mocha example uses CommonJS.
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Do I have to use Node’s built-in assert module?
No. It is the assertion library used in this tutorial; the Mocha runner and WebDriver setup do not depend on that specific assertion choice.
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