1 files changed, 19 insertions, 0 deletions
diff --git a/activerecord/test/cases/validations/uniqueness_validation_test.rb b/activerecord/test/cases/validations/uniqueness_validation_test.rb
index 56d8db0be9..71cb9d7b1e 100644
--- a/activerecord/test/cases/validations/uniqueness_validation_test.rb
+++ b/activerecord/test/cases/validations/uniqueness_validation_test.rb
@@ -35,6 +35,11 @@ class Employee < ActiveRecord::Base
   validates_uniqueness_of :nicknames
 end
 
+class TopicWithUniqEvent < Topic
+  belongs_to :event, foreign_key: :parent_id
+  validates :event, uniqueness: true
+end
+
 class UniquenessValidationTest < ActiveRecord::TestCase
   fixtures :topics, 'warehouse-things', :developers
 
@@ -376,4 +381,18 @@ class UniquenessValidationTest < ActiveRecord::TestCase
       assert_equal ["has already been taken"], e2.errors[:nicknames], "Should have uniqueness message for nicknames"
     end
   end
+
+  def test_validate_uniqueness_on_existing_relation
+    event = Event.create
+    assert TopicWithUniqEvent.create(event: event).valid?
+
+    topic = TopicWithUniqEvent.new(event: event)
+    assert_not topic.valid?
+    assert_equal ['has already been taken'], topic.errors[:event]
+  end
+
+  def test_validate_uniqueness_on_empty_relation
+    topic = TopicWithUniqEvent.new
+    assert topic.valid?
+  end
 end