nil response object in Rails 5.2, RSpec-Rails 3.7 spec for GET request

I've been heads down in this and feel like I'm probably making a simple mistake, but I haven't been able to find any information on this problem.

I have some request specs for Rails 5 and, when I test for a redirect--but not for a rendered template--I get an error, undefined method 'response_code' for nil:NilClass. The reason for this seems to be that @response is nil when the matcher is called (inside ActionDispatch::Assertions::ResponseAssertions code, not in my code). I am able to use cURL to make a request to the API and it returns a response as expected. The point where the error is returned is here (this is the ActionDispatch code):

def generate_response_message(expected, actual = @response.response_code)
  "Expected response to be a <#{code_with_name(expected)}>,"\
  " but was a <#{code_with_name(actual)}>"
  .dup.concat(location_if_redirected).concat(response_body_if_short)
end

Notice the first line, where the default value of the actual param is set to @response.response_code.

Here's my test code:

RSpec.describe "Admin registrations", type: :request do
  describe "new sign-up" do
    subject { get new_admin_registration_path }

    it "redirects to home" do
       expect(subject).to redirect_to(new_admin_session_path)
    end
  end
end

The relevant lines in the test log are:

Started GET "/admins/sign_up" for 127.0.0.1 at 2018-07-05 10:44:05 -0700
Processing by Admins::RegistrationsController#new as HTML
Redirected to http://example.org/admins/sign_in
Completed 301 Moved Permanently in 18ms (ActiveRecord: 0.0ms)

Interestingly, when I use byebug to check the value of subject, it does return a Rack::MockResponse object, so this is somehow not getting passed through.

Solution

I'm sure you've probably already solved this, but for anyone else who might stumble upon this, we ran into the same thing (response not being assigned after a request way made - either get or post, didn't try other methods, but assume they would all be the same). Existing request specs that had been working all started failing.

The culprit in our case was tracked down to a module that was required in rails_helper.rb, and added to rspec's config.include list:

config.include ApiHelper, type: request

Inside AppHelper was the root cause:

include Rack::Test::Methods

Commenting that line out (and ultimately for us, removing the entire helper as it wasn't really needed) restored the request specs to their previous, and working, state.

tl;dr:

Make sure you're not including Rack::Test::Methods in config.include for your rspec config inadvertently.