default_value_for_modified_test.rb

def test_default_values_are_not_changable_by_the_instances_when_dupable
  define_model_class do
    set_table_name "users"
    default_value_for :username, "hello"
  end
  user1 = TestClass.new
  user1.username << " world"
  user2 = TestClass.new
  assert_equal("hello", user2.username)
end

default_value_for_original_init.diff

-            __send__("#{attribute}=", container.evaluate(self))
+            value = container.evaluate(self)
+            value = value.dup if value.duplicable?
+            __send__("#{attribute}=", value)
             changed_attributes.delete(attribute)
           end
         end

default_value_for_original_test.rb

def test_default_values_are_not_duplicated
  define_model_class do
    set_table_name "users"
    default_value_for :username, "hello"
  end
  user1 = TestClass.new
  user1.username << " world"
  user2 = TestClass.new
  assert_equal("hello world", user2.username)
end