concurrent-starts-and-receive-notification.https.html

<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script src="/bluetooth/resources/bluetooth-test.js"></script>
<script src="/bluetooth/resources/bluetooth-fake-devices.js"></script>
<script>
'use strict';
let char;
bluetooth_test(() => {
  return setBluetoothFakeAdapter('HeartRateAdapter')
    .then(() => requestDeviceWithTrustedClick({
      filters: [{services: ['heart_rate']}]}))
    .then(device => device.gatt.connect())
    .then(gattServer => gattServer.getPrimaryService('heart_rate'))
    .then(service => service.getCharacteristic('heart_rate_measurement'))
    .then(characteristic => {
      char = characteristic;
      return Promise.all([
        characteristic.startNotifications(),
        characteristic.startNotifications()
      ]);
    })
    .then(() => {
      return new Promise(resolve => {
        let event_listener = () => {
          char.removeEventListener('characteristicvaluechanged', event_listener);
          resolve();
        };
        char.addEventListener('characteristicvaluechanged', event_listener);
      })
    });
}, 'Starting notification concurrently still can receive notification.');
</script>

chromium/third_party/blink/web_tests/wpt_internal/bluetooth/characteristic/notifications/concurrent-starts-and-receive-notification.https.html