error_responses.rb

# frozen_string_literal: true
module ErrorResponses
  def rails_respond_without_detailed_exceptions
    env_config = Rails.application.env_config
    original_show_exceptions = env_config['action_dispatch.show_exceptions']
    original_show_detailed_exceptions = env_config['action_dispatch.show_detailed_exceptions']
    env_config['action_dispatch.show_exceptions'] = true
    env_config['action_dispatch.show_detailed_exceptions'] = false
    yield
  ensure
    env_config['action_dispatch.show_exceptions'] = original_show_exceptions
    env_config['action_dispatch.show_detailed_exceptions'] = original_show_detailed_exceptions
  end
end

RSpec.configure do |config|
  config.include ErrorResponses
end

my_api_spec.rb

require 'rails_helper'

RSpec.describe 'My API' do
  let(:request) do
    lambda do
      get '/my_api/value-cannot-be-routed-due-to-route-constraints'
    end
  end

  context 'when action_dispatch.show_exceptions is false (default behavior on test env)' do
    it 'raise a routing error' do
      expect { request.call }.to raise_error(ActionController::RoutingError)
    end
  end
  
  context 'when action_dispatch.show_exceptions is true' do
    it 'return a 404' do
      rails_respond_without_detailed_exceptions do
        request.call
      end
      expect(response.status).to eq(404)
    end
  end
end