domains_spec.rb

require 'rails_helper'

RSpec.describe 'Domains Requests' do
  describe 'GET /api/domains/{id}' do

    it 'responds with the requested domain' do
      domain = FactoryGirl.create(:domain)

      get api_domain_path(domain)

      expect(response).to have_http_status(200)
    end
  end
end

response.status # => nil