Support enum attributes on validate_absence_of (#1464)

lib/shoulda/matchers/active_model/validate_absence_of_matcher.rb

@@ -109,6 +109,8 @@ module Shoulda
             end
           elsif array_column?
             ['an arbitary value']
+          elsif enum_column?
+            enum_values.first
           else
             case column_type
             when :integer, :float then 1
@@ -145,6 +147,15 @@ module Shoulda
             @subject.class.columns_hash[@attribute.to_s].respond_to?(:array) &&
             @subject.class.columns_hash[@attribute.to_s].array
         end
+
+        def enum_column?
+          @subject.class.respond_to?(:defined_enums) &&
+            @subject.class.defined_enums.key?(@attribute.to_s)
+        end
+
+        def enum_values
+          @subject.class.defined_enums[@attribute.to_s].values
+        end
       end
     end
   end

spec/unit/shoulda/matchers/active_model/validate_absence_of_matcher_spec.rb

@@ -91,6 +91,15 @@ describe Shoulda::Matchers::ActiveModel::ValidateAbsenceOfMatcher, type: :model
         end
       end
 
+      context 'when the column backing the attribute is an enum' do
+        it 'still works' do
+          model = define_model_validating_absence_of(:attr)
+          model.enum attr: %w[one two three]
+
+          expect(model.new).to validate_absence_of(:attr)
+        end
+      end
+
       context 'when used in the negative' do
         it 'fails' do
           assertion = lambda do