'Tests add_to_cart where the mode specified in the argument is NOT
in the database and NOT the default "audit".  In this case it
just adds the user in the CourseMode.DEFAULT_MODE for free.'

def test_add_with_default_mode(self):

    reg1 = PaidCourseRegistration.add_to_order(self.cart, self.course_key, mode_slug='DNE')
    self.assertEqual(reg1.unit_cost, 0)
    self.assertEqual(reg1.line_cost, 0)
    self.assertEqual(reg1.mode, CourseMode.DEFAULT_SHOPPINGCART_MODE_SLUG)
    self.assertEqual(reg1.user, self.user)
    self.assertEqual(reg1.status, 'cart')
    self.assertEqual(self.cart.total_cost, 0)
    self.assertTrue(PaidCourseRegistration.contained_in_order(self.cart, self.course_key))
    course_reg_code_item = CourseRegCodeItem.add_to_order(self.cart, self.course_key, 2, mode_slug='DNE')
    self.assertEqual(course_reg_code_item.unit_cost, 0)
    self.assertEqual(course_reg_code_item.line_cost, 0)
    self.assertEqual(course_reg_code_item.mode, CourseMode.DEFAULT_SHOPPINGCART_MODE_SLUG)
    self.assertEqual(course_reg_code_item.user, self.user)
    self.assertEqual(course_reg_code_item.status, 'cart')
    self.assertEqual(self.cart.total_cost, 0)
    self.assertTrue(CourseRegCodeItem.contained_in_order(self.cart, self.course_key))
