Fix enum attribute name verification

lib/shoulda/matchers/active_record/define_enum_for_matcher.rb

@@ -99,16 +99,12 @@ def expected_enum_values
           hashify(options[:expected_enum_values]).with_indifferent_access
         end
 
-        def enum_method
-          attribute_name.to_s.pluralize
-        end
-
         def actual_enum_values
-          model.class.send(enum_method)
+          model.class.send(attribute_name.to_s.pluralize)
         end
 
         def enum_defined?
-          model.class.respond_to?(enum_method)
+          model.defined_enums.keys.include?(attribute_name.to_s)
         end
 
         def enum_values_match?

spec/unit/shoulda/matchers/active_record/define_enum_for_matcher_spec.rb

@@ -2,6 +2,14 @@
 
 describe Shoulda::Matchers::ActiveRecord::DefineEnumForMatcher, type: :model do
   if active_record_supports_enum?
+    it "rejects a record when checking for enum's plural attribute name" do
+      message = "Expected #{record_with_array_values.class} to define :#{enum_attribute.to_s.pluralize} as an enum"
+
+      expect do
+        expect(record_with_array_values).to define_enum_for(enum_attribute.to_s.pluralize)
+      end.to fail_with_message(message)
+    end
+
     describe "with only the attribute name specified" do
       it "accepts a record where the attribute is defined as an enum" do
         expect(record_with_array_values).to define_enum_for(enum_attribute)