Test for HTTP status code in some RSpec rails request exampes, but for raised exception in others

Question

In a Rails 4.2.0 application tested with rspec-rails, I provide a JSON web API with a REST-like resource with a mandatory attribute mand_attr.

I'd like to test that this API answers with HTTP code 400 (BAD REQUEST) when that attribute is missing from a POST request. (See second example blow.) My controller tries to cause this HTTP code by throwing an ActionController::ParameterMissing, as illustrated by the first RSpec example below.

In other RSpec examples, I want raised exceptions to be rescued by the examples (if they're expected) or to hit the test runner, so they're displayed to the developer (if the error is unexpected), thus I do not want to remove

  # Raise exceptions instead of rendering exception templates.
  config.action_dispatch.show_exceptions = false

from config/environments/test.rb.

My plan was to have something like the following in a request spec:

describe 'POST' do
  let(:perform_request) { post '/my/api/my_ressource', request_body, request_header }
  let(:request_header) { { 'CONTENT_TYPE' => 'application/json' } }

  context 'without mandatory attribute' do
    let(:request_body) do
      {}.to_json
    end

    it 'raises a ParameterMissing error' do
      expect { perform_request }.to raise_error ActionController::ParameterMissing,
                                                'param is missing or the value is empty: mand_attr'
    end

    context 'in production' do
      ###############################################################
      # How do I make this work without breaking the example above? #
      ###############################################################
      it 'reports BAD REQUEST (HTTP status 400)' do
        perform_request
        expect(response).to be_a_bad_request
        # Above matcher provided by api-matchers. Expectation equivalent to
        #     expect(response.status).to eq 400
      end
    end
  end

  # Below are the examples for the happy path.
  # They're not relevant to this question, but I thought
  # I'd let you see them for context and illustration.
  context 'with mandatory attribute' do
    let(:request_body) do
      { mand_attr: 'something' }.to_json
    end

    it 'creates a ressource entry' do
      expect { perform_request }.to change(MyRessource, :count).by 1
    end

    it 'reports that a ressource entry was created (HTTP status 201)' do
      perform_request
      expect(response).to create_resource
      # Above matcher provided by api-matchers. Expectation equivalent to
      #     expect(response.status).to eq 201
    end
  end
end

I have found two working and one partially working solutions which I'll post as answers. But I'm not particularly happy with any of them, so if you can come up with something better (or just different), I'd like to see your approach! Also, if a request spec is the wrong type of spec to test this, I'd like to know so.

I foresee the question

Why are you testing the Rails framework instead of just your Rails application? The Rails framework has tests of its own!

so let me answer that pre-emptively: I feel I'm not testing the framework itself here, but whether I'm using the framework correctly. My controller doesn't inherit from ActionController::Base but from ActionController::API and I didn't know whether ActionController::API uses ActionDispatch::ExceptionWrapper by default or whether I first would have had to tell my controller to do so somehow.

Answer 1

You'd want to use RSpec filters for that. If you do it this way, the modification to Rails.application.config.action_dispatch.show_exceptions will be local to the example and not interfere with your other tests:

# This configure block can be moved into a spec helper
RSpec.configure do |config|
  config.before(:example, exceptions: :catch) do
    allow(Rails.application.config.action_dispatch).to receive(:show_exceptions) { true }
  end
end

RSpec.describe 'POST' do
  let(:perform_request) { post '/my/api/my_ressource', request_body }

  context 'without mandatory attribute' do
    let(:request_body) do
      {}.to_json
    end

    it 'raises a ParameterMissing error' do
      expect { perform_request }.to raise_error ActionController::ParameterMissing
    end

    context 'in production', exceptions: :catch do
      it 'reports BAD REQUEST (HTTP status 400)' do
        perform_request
        expect(response).to be_a_bad_request
      end
    end
  end
end

The exceptions: :catch is "arbitrary metadata" in RSpec speak, I chose the naming here for readability.