message: Mock up sendEvent by default
  The bridge lib now relies on it existing so it can add join guards to
  the returned Promise.
diff: @@ -42,6 +42,11 @@ function MockClient(config) {
  return Promise.resolve({});
  });
  + // mock up sendEvent
  + this.sendEvent.and.callFake(function() {
  + return Promise.resolve({});
  + });
  +
  // mock up getStateEvent immediately since it is called for every new IRC
  // connection.
  this.getStateEvent.and.callFake(function(roomId, type, skey, callback) {
  