add failing test for #566

spec/mobility/plugins/backend_spec.rb

@@ -112,10 +112,31 @@
         mod1 = translations_class.new("title", backend: backend_class_1)
         model_class.include mod1
 
-        Class.new(model_class)
+        # accessing mobility_backend_classes necessary to trigger parent freeze
+        Class.new(model_class).send(:mobility_backend_classes)
 
         expect(model_class.send(:mobility_backend_classes)).to be_frozen
       end
+
+      it "works with subclasses of subclasses" do
+        backend_class_1 = Class.new
+        backend_class_1.include Mobility::Backend
+
+        model_subclass = Class.new(model_class)
+        model_subclass_2 = Class.new(model_subclass)
+
+        # we specifically include translations after subclassing
+        mod1 = translations_class.new("title", backend: backend_class_1)
+        model_class.include mod1
+
+        title_backend_class_1 = model_class.mobility_backend_class("title")
+        title_backend_class_2 = model_subclass.mobility_backend_class("title")
+        title_backend_class_3 = model_subclass_2.mobility_backend_class("title")
+
+        expect(title_backend_class_1).to be <(backend_class_1)
+        expect(title_backend_class_2).to be <(backend_class_1)
+        expect(title_backend_class_3).to be <(backend_class_1)
+      end
     end
 
     describe "#mobility_backends" do