Fixes uniqueness matcher for enum columns

In Rails 4.1, if the scope from a validates_uniqueness_of matcher is an
enum, next_value won't get the correct value, then tests will fail even
that validation works. This adds a way to check if the scoped attribute
is an enum, and correctly get the next value.

NEWS.md

@@ -32,6 +32,8 @@
 * Fix `delegate_method` so that it does not stub the target method forever,
   returning it to its original implementation after the match ends.
 
+* Fix `validate_uniqueness_of` to work with Rails 4.1 enum columns.
+
 # 2.6.0
 
 * The boolean argument to `have_db_index`'s `unique` option is now optional, for

lib/shoulda/matchers/active_model/validate_uniqueness_of_matcher.rb

@@ -173,7 +173,12 @@ module Shoulda # :nodoc:
               previous_value ||= correct_type_for_column(@subject.class.columns_hash[scope.to_s])
 
               next_value =
-                if previous_value.respond_to?(:next)
+                if @subject.class.respond_to?(:defined_enums) && @subject.defined_enums[scope.to_s]
+                  available_values = @subject.defined_enums[scope.to_s].reject do |key, _|
+                    key == previous_value
+                  end
+                  available_values.keys.last
+                elsif previous_value.respond_to?(:next)
                   previous_value.next
                 elsif previous_value.respond_to?(:to_datetime)
                   previous_value.to_datetime.next

spec/shoulda/matchers/active_model/validate_uniqueness_of_matcher_spec.rb

@@ -122,6 +122,40 @@ describe Shoulda::Matchers::ActiveModel::ValidateUniquenessOfMatcher do
         not_to matcher.scoped_to(:fake)
     end
 
+    if rails_gte_4_1?
+      context 'when the scoped attribute is an enum' do
+        it 'accepts' do
+          expect(validating_scoped_uniqueness_with_enum([:scope1], scope1: 0)).
+            to matcher.scoped_to(:scope1)
+        end
+
+        context 'with a nil value' do
+          it 'accepts' do
+            expect(validating_scoped_uniqueness_with_enum([:scope1], scope1: nil)).
+              to matcher.scoped_to(:scope1)
+          end
+        end
+
+        context 'when too narrow of a scope is specified' do
+          it 'rejects' do
+            expect(validating_scoped_uniqueness_with_enum_with_two_scopes).
+              not_to matcher.scoped_to(:scope1, :scope2, :other)
+          end
+        end
+
+        context 'when too broad of a scope is specified' do
+          it 'rejects' do
+            expect(validating_scoped_uniqueness_with_enum_with_two_scopes).
+              not_to matcher.scoped_to(:scope1)
+          end
+        end
+
+        def validating_scoped_uniqueness_with_enum_with_two_scopes
+          validating_scoped_uniqueness_with_enum([:scope1, :scope2], scope1: 0, scope2: 0)
+        end
+      end
+    end
+
     context 'when the scoped attribute is a date' do
       it "accepts" do
         expect(validating_scoped_uniqueness([:scope1], :date, scope1: Date.today)).
@@ -250,6 +284,14 @@ describe Shoulda::Matchers::ActiveModel::ValidateUniquenessOfMatcher do
       model
     end
 
+    def validating_scoped_uniqueness_with_enum(*args)
+      attributes = args.extract_options!
+      model = define_scoped_model(*args)
+      model.enum scope1: [:foo, :bar]
+      create_existing_record(attributes)
+      model.new
+    end
+
     def validating_scoped_uniqueness_with_conflicting_next(*args)
       attributes = args.extract_options!
       model = define_scoped_model(*args).new