Improve failure message for unknown categories

spec/lib/api/every_api_endpoint_spec.rb

@@ -32,10 +32,21 @@
         next unless used_category
         next if used_category == :not_owned
 
-        [path, used_category] unless feature_categories.include?(used_category)
+        [klass, path, used_category] unless feature_categories.include?(used_category)
       end.compact
 
-      expect(routes_unknown_category).to be_empty, "#{routes_unknown_category.first(10)} had an unknown category"
+      message = -> do
+        list = routes_unknown_category.map do |klass, path, category|
+          "- #{klass} (#{path}): #{category}"
+        end
+
+        <<~MESSAGE
+          Unknown categories found for:
+          #{list.join("\n")}
+        MESSAGE
+      end
+
+      expect(routes_unknown_category).to be_empty, message
     end
 
     # This is required for API::Base.path_for_app to work, as it picks