title: undefined method `allow' for #<RSpec:: Rspec 3.6.0
body: <p>I'm new to Rails and specially to writing tests. I keep getting the error <code>undefined method allow</code> and <code>undefined method allow_any_instance_of'</code> when I run the test. 
  I've checked Rspec > 3 should accept the allow syntax, what is the issue in my code?</p>
  
  <pre><code>describe "GET #show" do
  
      let(:sample_json_list) {
        "{\"files\":[{\"title\":\"discourse-2017-08-24-085545-v20170803123704.sql.gz\",\"id\":\"0B7WjYjWZJv_4MENlYUM2SjkyU1E\",\"size\":\"14070939\",\"created_at\":\"2017-08-24T06:56:21.698+00:00\"}]}"
      }
  
      before {
        allow_any_instance_of(DiscourseDownloadFromDrive::DriveDownloader).to receive(:json_list).and_return(sample_json_list)
      }
  
      it "renders the json" do
        get :show
        response.body.should == sample_json_list
      end
  
    end
  </code></pre>