title: Why is this test failing - Not Implemented Error Rspec 3.1.x and Rails 4.1.9
body: <p>I am testing the following method:</p>
  
  <pre><code>  def deal_with_response(site, responses, request_url)
      response.each do |response|
        if response.code == 200
          send_request(site.site_api_url, site.site_api_key, response, request_url)
        elsif response.code == 404
          send_request(site.site_api_url, site.site_api_key, response, request_url)
          GeneralMailer.recieved_404(ENV['ADMINISTRATOR_NAME'], ENV['ADMINISTRATOR_EMAIL'], site, response).deliver_now
        elsif response.code == 500
          send_request(site.site_api_url, site.site_api_key, response, request_url)
          GeneralMailer.recieved_500(ENV['ADMINISTRATOR_NAME'], ENV['ADMINISTRATOR_EMAIL'], site, response).deliver_now
        else
          send_request(site.site_api_url, site.site_api_key, response, request_url)
          GeneralMailer.recieved_error(ENV['ADMINISTRATOR_NAME'], ENV['ADMINISTRATOR_EMAIL'], site, response).deliver_now
        end
      end
    end
  </code></pre>
  
  <p>Which is tested by this code:</p>
  
  <pre><code>it "should send no email (200)" do
    response = double("response", :code =&gt; 200)
    site = double("site", :site_api_url =&gt; 'http://google.ca', site_api_key: 'sdsadsasada')
    send_request_method = double()
    send_request_method.stub(:send_request).with(site.site_api_url, site.site_api_key, [response], 'http://google.ca').and_return nil
  
    expect{ BlackBird::PublishToSites::User.deal_with_response(response) }.to_not change{ ActionMailer::Base.deliveries.count }.by(1)
  end
  </code></pre>
  
  <p>The result is:</p>
  
  <pre><code> Failure/Error: expect{ BlackBird::PublishToSites::User.deal_with_response(response) }.to_not change{ ActionMailer::Base.deliveries.count }.by(1)
   NotImplementedError:
     `expect { }.not_to change { }.by()` is not supported
   # ./spec/blackbird/publish_to_sites/user_spec.rb:129:in `(root)'
  </code></pre>
  
  <p>Am I missing something? I was doing similar code like this in other tests and it works fine. Did I dod the expect block wrong?</p>