explicitly reset registries on reload

config/initializers/acts_as_favorable.rb

@@ -4,6 +4,7 @@
 # as no eager loading takes place
 Rails.application.config.to_prepare do
   OpenProject::Acts::Favorable::Registry.add(
-    Project
+    Project,
+    reset: true
   )
 end

config/initializers/acts_as_watchable.rb

@@ -10,6 +10,7 @@
     News,
     Wiki,
     WikiPage,
-    WorkPackage
+    WorkPackage,
+    reset: true
   )
 end

lib_static/open_project/acts/registry_methods.rb

@@ -33,10 +33,12 @@ def instance(model_name)
         models[model_name.singularize.camelize]
       end
 
-      def add(*models)
+      def add(*models, reset: false)
         instance_methods_module = module_parent.const_get(:InstanceMethods)
         acts_as_method_name = "acts_as_#{module_parent_name.demodulize.underscore}"
 
+        self.models.clear if reset
+
         models.each do |model|
           unless model.ancestors.include?(instance_methods_module)
             raise ArgumentError.new("Model #{model} does not include #{acts_as_method_name}")

spec/lib/acts_as_watchable/lib/open_project/acts/registry_methods_spec.rb

@@ -86,5 +86,26 @@ def described_module = described_class
         expect(registry.instance("models")).to eq(reloaded_model)
       end
     end
+
+    describe "after registry reset" do
+      let(:other_model) { Class.new }
+
+      before do
+        other_model.include instance_methods_module
+
+        allow(other_model).to receive(:name).and_return("OtherModel")
+
+        registry.add(model)
+        registry.add(other_model, reset: true)
+      end
+
+      it "doesn't return model registered before reset" do
+        expect(registry.instance("models")).to be_nil
+      end
+
+      it "returns model registered after reset" do
+        expect(registry.instance("other_models")).to eq(other_model)
+      end
+    end
   end
 end