Merge pull request rails#6324 from acapilleri/dup_validation_3_2

Dup validation 3 2

Author: rafaelfranca

activemodel/lib/active_model/validations.rb

@@ -165,6 +165,12 @@ def inherited(base)
       end
     end
 
+    # Clean the +Errors+ object if instance is duped
+    def initialize_dup(other) # :nodoc:
+       @errors = nil
+       super
+    end
+
     # Returns the +Errors+ object that holds all information about attribute error messages.
     def errors
       @errors ||= Errors.new(self)

activemodel/test/cases/validations_test.rb

@@ -339,4 +339,19 @@ def test_strict_validation_error_message
     end
     assert_equal "Title can't be blank", exception.message
   end
+
+  def test_dup_validity_is_independent
+    Topic.validates_presence_of :title
+    topic = Topic.new("title" => "Litterature")
+    topic.valid?
+
+    duped = topic.dup
+    duped.title = nil
+    assert duped.invalid?
+
+    topic.title = nil
+    duped.title = 'Mathematics'
+    assert topic.invalid?
+    assert duped.valid?
+  end
 end