Respond to all formats with html

app/controllers/errors_controller.rb

@@ -9,7 +9,7 @@ class ErrorsController < ApplicationController
 
       event.add_metadata(:request, request.env)
     end
-    render status: :not_found
+    render "not_found", status: :not_found, formats: :html
   end
 
   def internal_server_error

spec/requests/errors_spec.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Errors', type: :request do
+  include ExceptionHelper
+
+  shared_examples "returning a HTTP 404" do |path|
+    it path do
+      rails_respond_without_detailed_exceptions do
+        get path
+      end
+
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  it_behaves_like "returning a HTTP 404", "/nonexistent/path"
+  it_behaves_like "returning a HTTP 404", "/nonexistent/path.jpg"
+  it_behaves_like "returning a HTTP 404", "/nonexistent/path.xml"
+end

spec/support/request/exception_helper.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+# https://medium.com/@edgar/rspec-how-to-have-rails-request-specs-handling-errors-like-production-a8c21ed0308a
+module ExceptionHelper
+  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