new_contents: import unittest
  from cal import Calculator
  
  
  class TddInPythonExample(unittest.TestCase):
   
      def test_calculator_add_method_returns_correct_result(self):
      	
          calc = Calculator()
          result = calc.add(2,2)
          self.assertEqual(4, result)
      def test_calculator_returns_error_message_if_both_args_not_numbers(self):
      	calc = Calculator()
          self.assertRaises(ValueError, calc.add, '2', '3')
  
  if __name__ == '__main__':
      unittest.main()
  
subject: Create testcase.py