Getting error in Ember Acceptance test

In ember, I'm writing acceptance test for a template using pretender as mock server.

var server = new Pretender();
server.get('/events', JSON.stringify(200, {
  events: [
    {
      event_id: '23456789098765',
      event_time: '2017-02-01',
      event_time_formatted: '01/02/2017 06:24 AM',
      event_type: 'renewed'
    }
  ]
}));

When I run the ember test I'm getting "Unable to connect to server. Please check your network connection." error!

Can anybody tell why this happening?