Testing Rails 404 and 500 JSON reponse - ruby-on-rails

Question

I am building a JSON backend API with Rails, and I can't seem to figure this out: How can one test using RSpec the Rails default error responses? For example, for a generic 404 request, I currently have the following request spec:
require 'rails_helper'
RSpec.describe '404 errors' do
let(:json) { JSON.parse(response.body) }
before { get '/noexistent', headers: headers }
# examples
end
Rails, however, refuses to render the 404 response that it would normally yield, instead simply raising:
ActionController::RoutingError:
  No route matches [GET] "/404"
I've tried removing config.consider_all_request_local = true from config/environments/test.rb, with no results.
Note that I've seen this question (it's where I got the idea for consider_all_requests_local), but it applies to development, not testing.
EDIT: I am using config.exceptions_app = self.routes to redirect errors to an ErrorsController. This works fine in development or production, but not while testing. When testing, I still get the above error. Any ideas?

Answer 1

It turns out the answer was rather simple. I had to change this line in config/environments/test.rb:
# Raise exceptions instead of rendering exception templates.
config.action_dispatch.show_exceptions = false
to:
# Do not raise exceptions instead of rendering exception templates.
config.action_dispatch.show_exceptions = true