function completeForwardChannel(
    serverVersion = undefined, hostPrefix = undefined) {
  const responseData = '[[0,["c","1234567890ABCDEF",' +
      (hostPrefix ? `"${hostPrefix}"` : 'null') +
      (serverVersion ? `,${serverVersion}` : '') + ']]]';
  channel.onRequestData(getSingleForwardRequest(), responseData);
  channel.onRequestComplete(getSingleForwardRequest());
  mockClock.tick(0);
}
@param {number=} serverVersion
@param {string=} hostPrefix