Convert "custom css" controller spec to request spec (#31595)

spec/controllers/custom_css_controller_spec.rb

@@ -1,19 +0,0 @@
-# frozen_string_literal: true
-
-require 'rails_helper'
-
-describe CustomCssController do
-  render_views
-
-  describe 'GET #show' do
-    before do
-      get :show
-    end
-
-    it 'returns http success' do
-      expect(response).to have_http_status(200)
-    end
-
-    it_behaves_like 'cacheable response'
-  end
-end

spec/requests/custom_stylesheets_spec.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe 'Custom stylesheets' do
+  describe 'GET /custom.css' do
+    before { get '/custom.css' }
+
+    it 'returns http success' do
+      expect(response)
+        .to have_http_status(200)
+        .and have_attributes(
+          content_type: match('text/css')
+        )
+    end
+
+    it_behaves_like 'cacheable response'
+  end
+end