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Test Runner: Commands

Commands for executing code server-side during your tests in the browser. To control the browser page, access the file system, or execute NodeJS libraries.

Built-in commands can change the viewport, emulate media queries or set the user agent. You can create custom commands to implement your own functionalities.

Usage

Install the library:

npm i --save-dev @web/test-runner-commands

Built-in commands

You can use the built-in commands directly in your tests.

Viewport

The setViewport command allows changing the browser's viewport in a test. The function is async and should be awaited.

setViewport is supported in @web/test-runner-chrome, -puppeteer and -playwright.

View example
import { setViewport } from '@web/test-runner-commands';

describe('my component', () => {
  it('works on 360x640', async () => {
    await setViewport({ width: 360, height: 640 });
    console.log(window.innerWidth); // 360
    console.log(window.innerHeight); // 640
  });

  it('works on 400x800', async () => {
    await setViewport({ width: 400, height: 800 });
    console.log(window.innerWidth); // 400
    console.log(window.innerHeight); // 800
  });
});

Emulate media

The emulateMedia command allows changing browser media queries. The function is async and should be awaited.

emulateMedia is supported in @web/test-runner-chrome, -puppeteer and -playwright. The reducedMotion option is not supported by playwright.

View example
import { emulateMedia } from '@web/test-runner-commands';

it('can emulate print media type', async () => {
  await emulateMedia({ media: 'print' });
  expect(matchMedia('print').matches).to.be.true;
  await emulateMedia({ media: 'screen' });
  expect(matchMedia('screen').matches).to.be.true;
});

it('can emulate color scheme', async () => {
  await emulateMedia({ colorScheme: 'dark' });
  expect(matchMedia('(prefers-color-scheme: dark)').matches).to.be.true;
  await emulateMedia({ colorScheme: 'light' });
  expect(matchMedia('(prefers-color-scheme: light)').matches).to.be.true;
});

// The reducedMotion option is not supported by playwright.
it('can emulate reduced motion', async () => {
  await emulateMedia({ reducedMotion: 'reduce' });
  expect(matchMedia('(prefers-reduced-motion: reduce)').matches).to.be.true;
  await emulateMedia({ reducedMotion: 'no-preference' });
  expect(matchMedia('(prefers-reduced-motion: no-preference)').matches).to.be.true;
});

Send keys

The sendKeys command will cause the browser to press keys or type a sequence of characters as if it received those keys from the keyboard. This greatly simplifies interactions with form elements during test and surfaces the ability to directly inspect the way focus flows through test content in response to the Tab key. The function is async and should be awaited.

The sendKeys command accepts an object with exactly one of the following properties being set, each of which trigger a specific keyboard action:

  • type - Types a sequence of characters. type is not affected by modifier keys, holding Shift will not type the text in upper-case.
  • press - Presses a single key, resulting in a key down, and a key up. press is affected by modifier keys, holding Shift will type the text in upper-case. See below for key reference.
  • down - Holds down a single key. See below for key reference.
  • up - Releases a single key. See below for key reference.

Multiple calls of the sendKeys command can be used to trigger key combinations. For example sending a down command with the value Shift, and then sending a press command with the value Tab will effectively trigger a Shift+Tab.

sendKeys is supported in @web/test-runner-chrome, -puppeteer and -playwright. All commands are simple wrappers around the respective APIs in the supported test runners. Please refer to their respective docs for detailed behavior, and which specific strings can be used for the press, down and up commands:

View example
import { sendKeys } from '@web/test-runner-commands';

it('natively types into an input', async () => {
  const keys = 'abc123';
  const input = document.createElement('input');
  document.body.append(input);
  input.focus();

  await sendKeys({
    type: keys,
  });

  expect(input.value).to.equal(keys);
  input.remove();
});

it('natively presses `Tab`', async () => {
  const input1 = document.createElement('input');
  const input2 = document.createElement('input');
  document.body.append(input1, input2);
  input1.focus();
  expect(document.activeElement).to.equal(input1);

  await sendKeys({
    press: 'Tab',
  });

  expect(document.activeElement).to.equal(input2);
  input1.remove();
  input2.remove();
});

it('natively presses `Shift+Tab`', async () => {
  const input1 = document.createElement('input');
  const input2 = document.createElement('input');
  document.body.append(input1, input2);
  input2.focus();
  expect(document.activeElement).to.equal(input2);

  await sendKeys({
    down: 'Shift',
  });
  await sendKeys({
    press: 'Tab',
  });
  await sendKeys({
    up: 'Shift',
  });

  expect(document.activeElement).to.equal(input1);
  input1.remove();
  input2.remove();
});

it('natively holds and then releases a key', async () => {
  const input = document.createElement('input');
  document.body.append(input);
  input.focus();

  await sendKeys({
    down: 'Shift',
  });
  // Note that pressed modifier keys are only respected when using `press` or
  // `down`, and only when using the `Key...` variants.
  await sendKeys({
    press: 'KeyA',
  });
  await sendKeys({
    press: 'KeyB',
  });
  await sendKeys({
    press: 'KeyC',
  });
  await sendKeys({
    up: 'Shift',
  });
  await sendKeys({
    press: 'KeyA',
  });
  await sendKeys({
    press: 'KeyB',
  });
  await sendKeys({
    press: 'KeyC',
  });

  expect(input.value).to.equal('ABCabc');
  input.remove();
});

Set user agent

The setUserAgent command changes the browser's user agent. The function is async and should be awaited.

setUserAgent is supported in @web/test-runner-chrome and -puppeteer

View example
import { setUserAgent } from '@web/test-runner-commands';

it('can set the user agent', async () => {
  const userAgent = 'my custom user agent';
  expect(navigator.userAgent).to.not.equal(userAgent);
  await setUserAgent(userAgent);
  expect(navigator.userAgent).to.equal(userAgent);
});

Snapshots

The snapshot commands allow comparing, saving and retrieving snapshots. The snapshot comparison implementation is very basic and does not include any integration with assertion libraries.

The getSnapshotConfig and compareSnapshot functions use the updateSnapshots option which can be passed to the snapshotsPlugin. When using the regular @web/test-runner package, it can be configured using the --update-snapshots CLI flag.

View example
import {
  getSnapshotConfig,
  getSnapshots,
  getSnapshot,
  saveSnapshot,
  removeSnapshot,
  compareSnapshot,
} from '@web/test-runner-commands';

it('can compare snapshots', async () => {
  await compareSnapshot({ name: 'my-snapshot', content: 'my snapshot content' });
});

it('can use raw snapshot commands', async () => {
  // the config contains a boolean whether updating snapshots is enabled, this can be used by assertion
  // library plugins to decide to overwrite the existing snapshot
  const config = await getSnapshotConfig();
  console.log(config.updateSnapshots);

  // returns all the snapshots defined for this test file
  const snapshots = await getSnapshots();

  // returns the stored snapshot for this file with this name
  const snapshot = await getSnapshot({ name: 'my-snapshot' });

  // saves snapshot with this name and content
  await saveSnapshot({ name: 'my-snapshot', content: 'my snapshot content' });

  // removes snapshot with this name
  await removeSnapshot({ name: 'my-snapshot' });
});

File commands are supported in all test runner browsers.

Writing and reading files

The file commands allow writing, reading and removing files. The specified path is resolved relative to the test file being executed.

View example
import { writeFile, readFile, removeFile } from '@web/test-runner-commands';

it('can use file commands', async () => {
  await writeFile('test-data/hello-world.txt', 'Hello world!');

  const content = await readFile('test-data/hello-world.txt');
  console.log(content); // 'Hello world!'

  await removeFile('test-data/hello-world.txt');
});

File commands are supported in all test runner browsers.

Accessibility Snapshot

The a11ySnapshot command requests a snapshot of the accessibility tree built in the browser representing the current page or the tree rooter by the passed selector property. The function is async and should be awaited.

a11ySnapshot is supported in @web/test-runner-chrome, -puppeteer and -playwright.

View example
import { a11ySnapshot, findAccessibilityNode } from '@web/test-runner-commands';

it('returns an accessibility tree with appropriately labelled element in it', async () => {
  const buttonText = 'Button Text';
  const labelText = 'Label Text';
  const fullText = `${labelText} ${buttonText}`;
  const role = 'button';

  const label = document.createElement('label');
  label.textContent = labelText;
  label.id = 'label';
  const button = document.createElement('button');
  button.textContent = buttonText;
  button.id = 'button';
  button.setAttribute('aria-labelledby', 'label button');
  document.body.append(label, button);

  const snapshot = await a11ySnapshot();
  const foundNode = findAccessibilityNode(
    snapshot,
    node => node.name === fullText && node.role === role,
  );
  expect(foundNode, 'A node with the supplied name has been found.').to.not.be.null;

  label.remove();
  button.remove();
});

Custom commands

To create a custom command, you first need to add a test runner plugin which implements the executeCommand function.

This function receives the currently executing command, optional command payload from the browser, and the associated test session. The command runs on the server, giving you access to things like the browser launcher, file system, or any NodeJS libraries you want to use.

By returning a non-null or undefined value from this function, the test runner will assume you have processed it, not call any other plugins and return the return value to the browser. The function can be async.

View example
import fs from 'fs';

function myPlugin() {
  return {
    name: 'my-plugin',

    executeCommand({ command, payload }) {
      if (command === 'my-command') {
        // write the data receives from the browser to a disk
        fs.writeFileSync('./my-file.json', JSON.stringify(payload));
        // by returning a value, we signal the test runner we've handled this command
        return true;
      }
    },
  };
}

// your web-test-runner.config.js
export default {
  plugins: [myPlugin()],
};

The executeCommand function receives the current test session, you can use this to access the browser launcher instance for advanced functionalities not available from the browser. Because there are different kinds of browser launchers, you need to use the type property to adjust the behavior of your plugin.

View example
export function takeScreenshotPlugin() {
  return {
    name: 'take-screen-command',

    async executeCommand({ command, payload, session }) {
      if (command === 'take-screenshot') {
        // handle specific behavior for puppeteer
        if (session.browser.type === 'puppeteer') {
          const page = session.browser.getPage(session.id);
          const screenshot = await page.screenshot();
          // do something with the screenshot
          return true;
        }

        // handle specific behavior for playwright
        if (session.browser.type === 'playwright') {
          const page = session.browser.getPage(session.id);
          const screenshot = await page.screenshot();
          // do something with the screenshot
          return true;
        }

        // you might not be able to support all browser launchers
        throw new Error(
          `Taking screenshots is not supported for browser type ${session.browser.type}.`,
        );
      }
      return false;
    },
  };
}

After implementing your plugin, it can be called from the browser using the executeServerCommand function. Any data passed in the second parameter is received by the server plugin. It should be serializable to JSON.

View example
import { executeServerCommand } from '@web/test-runner-commands';

it('my test', async () => {
  await executeServerCommand('my-command');
  // optionally pass in serializable data
  await executeServerCommand('my-command', { foo: 'bar' });
});