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Test Automation Recipes

Mock microphone input

Use case: your app records the user’s voice — speech-to-text, a voice memo, a language-learning app grading pronunciation, an audio level meter. You want an automated test that speaks into the microphone.

Why this is hard

Section titled “Why this is hard”

Playwright has no API for microphone input. The workarounds you’ll find have sharp edges:

  • --use-file-for-fake-audio-capture is Chromium-only, accepts WAV only, and the file is fixed at browser launch — you can’t say one thing on the first screen and another thing later.
  • Piping audio through a real OS-level virtual device works but is miserable in CI.

Recipe

Section titled “Recipe”

playwright-audio-mocking replaces navigator.mediaDevices.getUserMedia before the page loads and backs it with a real Web Audio MediaStream. Anything downstream — MediaRecorder, AnalyserNode, WebRTC, speech APIs — works unmodified, on Chromium, Firefox and WebKit.

Terminal window
npm install -D playwright-audio-mocking
import { test, expect } from '@playwright/test';
import { mockMicrophone } from 'playwright-audio-mocking';


test('transcribes speech', async ({ page }) => {
  const mic = await mockMicrophone(page);   // install BEFORE page.goto()
  await page.goto('/voice-memo');


  await page.getByRole('button', { name: 'Record' }).click();
  await mic.play('tests/fixtures/hello-world.wav');  // stream into the mic
  await mic.waitForEnd();
  await page.getByRole('button', { name: 'Stop' }).click();


  await expect(page.getByTestId('transcript')).toContainText('hello world');
});

Runtime control

Section titled “Runtime control”

Unlike launch-time flags, playback is fully scriptable mid-test:

await mic.play('fixtures/greeting.mp3');            // any format the browser decodes
await mic.play('fixtures/question.mp3');            // switch files mid-stream
await mic.play('fixtures/hold-music.mp3', { loop: true });
await mic.pause();                                  // silence, position kept
await mic.resume();
await mic.stop();                                   // silence, position reset


const { playing, position, duration } = await mic.status();

Generated speech, no fixture files

Section titled “Generated speech, no fixture files”

Pass bytes instead of a path — for example straight from a TTS API, so each test can say something unique:

await mic.play(Buffer.from(await synthesizeSpeech('add milk to my shopping list')));

Caveats

Section titled “Caveats”
  • Call mockMicrophone(page) before page.goto() — it’s injected as an init script.
  • On Chromium, launch with RECOMMENDED_CHROMIUM_ARGS (--autoplay-policy=no-user-gesture-required) so Web Audio can start without a user gesture.
  • The mock replaces the audio track only; getUserMedia({ audio, video }) passes the video constraint through to the real implementation by default.
Section titled “Related”