Move dup destroyed test to specific file that tests dup logic

Also change other related test to use existing record rather than
creating new one.

activerecord/test/cases/dup_test.rb

@@ -32,6 +32,14 @@ module ActiveRecord
       assert duped.new_record?, 'topic is new'
     end
 
+    def test_dup_not_destroyed
+      topic = Topic.first
+      topic.destroy
+
+      duped = topic.dup
+      assert_not duped.destroyed?
+    end
+
     def test_dup_has_no_id
       topic = Topic.first
       duped = topic.dup

activerecord/test/cases/persistence_test.rb

@@ -234,19 +234,12 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_save_with_duping_of_destroyed_object
-    developer = Developer.create(name: "Kuldeep")
+    developer = Developer.first
     developer.destroy
     new_developer = developer.dup
     new_developer.save
     assert new_developer.persisted?
-  end
-
-  def test_dup_of_destroyed_object_is_not_destroyed
-    developer = Developer.create(name: "Kuldeep")
-    developer.destroy
-    new_developer = developer.dup
-    new_developer.save
-    assert_equal new_developer.destroyed?, false
+    assert_not new_developer.destroyed?
   end
 
   def test_create_many