Run end-to-end tests in a web browser
Last updated 2 years ago by keithkml .
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$ cnpm install ottr 
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Easy, robust end-to-end UI tests for web apps.


  • Write once, run in every web browser (Chrome, Firefox, IE, Edge, Safari, iOS, Android)
  • Super robust. Does not use Selenium or Chrome DevTools or Electron or anything special
  • Can run tests against your local development server or production server
  • Can be used as a command-line test runner (requires headless browser)
  • Web-based UI for:
    • Interactively debugging tests in your browser of choice
    • Built-in test authoring REPL for rapid development of new test cases
  • Automatically takes screenshots and records all network requests

Installation and Usage

Assuming you have a npm run watch script in your project, which starts your web server on port 3000:

npm install --save-dev ottr
node_modules/.bin/ottr --server 'npm run watch' localhost:3000 src/test/e2e/index.js

Then just visit the URL printed to the console (defaults to http://localhost:50505/ottr/ui)

Command Line Reference

Usage: ottr [options] <url> <file>

  url:  the website to run your tests against
  file: root end-to-end test file that runs all your tests


  -s, --server <cmd>     command ottr uses to launch your server, e.g. 'npm run watch'
  -c, --chrome           opens headless Chrome/Chromium to the ottr UI to run your tests
  --chromium <path>      uses the specified Chrome/Chromium binary to run your tests
  --host <ip>            Chrome will use this hostname or IP address instead of localhost
  --coverage <type>      use 'chrome' for code coverage from Chrome DevTools (see below)
  --screenshots          take screenshots every 100ms
  --concurrency <n>      number of tests ottr should run in simultaneous iframes
  --wait-timeout <secs>  max server startup wait time (see --wait-path)
  --wait-path <path>     wait for your server to return 200 for this path (e.g., /health)
  -d, --debug            keep ottr running indefinitely after tests finish
  -i, --inspect          runs Chrome in GUI mode so you can watch tests run interactively
  -h, --help             output usage information


ottr tests are written using a wrapper around tape, a simple yet powerful testing and assertion library.

import {setValue, sleep, test} from 'ottr';
import $ from 'jquery';

test('searching for uuid works', '/', async t => {
  setValue($('.searchBox input')[0], 'doctor');
  await sleep(500);
  t.equal($('.result').text(), 'Doctor Seuss');

Command-Line Examples

  $ ottr --chrome --debug localhost:9999 src/test/e2e.js

Runs your tests in e2e.js against your local development server using a headless Chrome browser. The --debug option leaves ottr running so you can debug interactively using the browser of your choice. (Your server must already be running on port 9999.)

  $ nyc --reporter=html ottr --coverage=chrome dist-test/e2e.js

Runs your tests against Google's home page, in a Chrome headless browser, with Chrome's built-in code coverage recording. nyc (the istanbul command-line tool) generates an HTML coverage report.

Under the Hood

How does ottr work?

ottr's main benefit is that it runs your test code inside your web app itself, rather than in a separate browser window or Node process.

However, this gets a little tricky because of web standards, particularly cross-origin protections. To bypass browser security, ottr:

  • Sets up a full HTTP proxy to the website you're testing (via http-proxy-middleware)
  • Injects your test code into the page at the network level (via webpack)


We'd love for you to contribute to this project. Before we can accept your contributions, we kindly ask you to sign our Uber Contributor License Agreement.

  • If you find a bug, please open an issue, or submit a fix via a pull request
  • If you have a feature request, open an issue, or submit an implementation via a pull request
  • If you want to contribute, submit a pull request


Current Tags

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