firefox/testing/web-platform/tests/serial/serialPort_disconnect-manual.https.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title></title>
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <script src="resources/common.js"></script>
    <script src="resources/manual.js"></script>
  </head>
  <body>
    <p>
      These tests require a serial device to be connected and disconnected.
    </p>
    <script>
      manual_serial_test(async (t, port) => {
        const watcher = new EventWatcher(t, navigator.serial, ['disconnect']);

        await port.open({baudRate: 115200, bufferSize: 1024});

        const disconnectPromise = watcher.wait_for(['disconnect'])
        const reader = port.readable.getReader();

        const disconnectMessage = document.createElement('div');
        disconnectMessage.textContent = 'Disconnect the device now.';
        document.body.appendChild(disconnectMessage);

        try {
          while (true) {
            const {value, done} = await reader.read();
            // Ignore |value| in case the device happens to produce data. It is
            // not important for this test.
            assert_false(done);
          }
        } catch (e) {
          assert_equals(e.constructor, DOMException);
          assert_equals(e.name, 'NetworkError');
        }
        reader.releaseLock();
        assert_equals(port.readable, null);

        let event = await disconnectPromise;
        assert_equals(event.target, port);

        disconnectMessage.remove();

        await port.close();
      }, 'Disconnect during read is detected.');

      manual_serial_test(async (t, port) => {
        const watcher = new EventWatcher(t, navigator.serial, ['disconnect']);

        await port.open({baudRate: 115200, bufferSize: 1024});

        const disconnectPromise = watcher.wait_for(['disconnect'])
        const writer = port.writable.getWriter();

        const disconnectMessage = document.createElement('div');
        disconnectMessage.textContent = 'Disconnect the device now.';
        document.body.appendChild(disconnectMessage);

        const data = new Uint8Array(4096);
        try {
          while (true) {
            await writer.write(data);
          }
        } catch (e) {
          assert_equals(e.constructor, DOMException);
          assert_equals(e.name, 'NetworkError');
        }
        writer.releaseLock();
        assert_equals(port.writable, null);

        let event = await disconnectPromise;
        assert_equals(event.target, port);

        disconnectMessage.remove();

        await port.close();
      }, 'Disconnect during write is detected.');
    </script>
  </body>
</html>