Improve delegation test coverage

lib/ams/delegatable.rb

@@ -1,5 +1,7 @@
 module AMS
   module Delegatable
+    KERNEL_METHOD_METHOD = ::Kernel.instance_method(:method)
+
     # delegate constant lookup to Object
     def const_missing(name)
       ::Object.const_get(name)
@@ -12,6 +14,10 @@ module AMS
           __send__(*args)
         end
 
+        def method(method_name)
+          AMS::Delegatable::KERNEL_METHOD_METHOD.bind(self).call(method_name)
+        end
+
         private
 
         def method_missing(name, *args, &block)
@@ -21,16 +27,6 @@ module AMS
         def respond_to_missing?(name, include_private = false)
           object.respond_to?(name, include_private)
         end
-
-        const_set(:KERNEL_METHOD_METHOD, ::Kernel.instance_method(:method))
-        def method_handle_for(method_name)
-          KERNEL_METHOD_METHOD.bind(self).call(method_name)
-        rescue NameError => original
-          handle = self.method(method_name)
-          raise original unless handle.is_a? Method
-          handle
-        end
-        alias method method_handle_for
       end
     end
   end

test/unit/serializer/object_delegation_test.rb

@@ -5,6 +5,7 @@ module AMS
   class Serializer
     class ObjectDelegationTest < Test
       class ParentModelSerializer < Serializer
+        attribute :some_method
       end
 
       def setup
@@ -26,6 +27,29 @@ module AMS
       def test_model_delegates_respond_to_object
         refute @serializer_instance.respond_to?(:not_delegated?)
       end
+
+      def test_model_delegates_respond_to_missing_to_object
+        refute @serializer_instance.respond_to?(:not_delegated?)
+      end
+
+      def test_serializer_binds_method_method
+        file, = @serializer_instance.method(:some_method).source_location
+        assert_match(%r{/lib/ams/serializer.rb\z}, file)
+      end
+
+      def test_serializer_instance_raises_method_missing
+        exception = assert_raises(NameError) do
+          @serializer_instance.non_existent_method
+        end
+        assert_match(%r{undefined method `non_existent_method' for #<ParentModel:[^@]+@id=1>\z}, exception.message)
+      end
+
+      def test_serializer_object_raises_method_missing
+        exception = assert_raises(NameError) do
+          @serializer_instance.method(:non_existent_method)
+        end
+        assert_match(%r{undefined method `non_existent_method' for class `AMS::Serializer::ObjectDelegationTest::ParentModelSerializer'\z}, exception.message)
+      end
     end
   end
 end