new_contents: import unittest
  
  from eqtools import eval_postfix_expr
  from schema_provider import SYM_XOR, SYM_XNOR, SYM_AND, SYM_NAND, SYM_NOR
  from schema_provider import SYM_OR
  
  
  class TestEvaluatePostfixExpr(unittest.TestCase):
      """
      Testing for this function is fairly simple because we are using a proven
      algorithm and all input is assumed to be well-formed.
      """
  
      # === Helper Methods ======================================================
      def helper_test_postfix_expr(self, expr_to_eval="", expected_result=-1):
          self.assertEqual(expected_result, eval_postfix_expr(expr_to_eval))
  
      # === Test Methods ========================================================
      def test_two_operands_xor(self):
          input_pairs = ["00", "01", "10", "11"]
          expected_results = [0, 1, 1, 0]
          for input_pair, expected_result in zip(input_pairs, expected_results):
              self.helper_test_postfix_expr(
                  expr_to_eval=input_pair+SYM_XOR,
                  expected_result=expected_result
              )
  
      def test_two_operands_xnor(self):
          input_pairs = ["00", "01", "10", "11"]
          expected_results = [1, 0, 0, 1]
          for input_pair, expected_result in zip(input_pairs, expected_results):
              self.helper_test_postfix_expr(
                  expr_to_eval=input_pair+SYM_XNOR,
                  expected_result=expected_result
              )
  
      def test_two_operands_and(self):
          input_pairs = ["00", "01", "10", "11"]
          expected_results = [0, 0, 0, 1]
          for input_pair, expected_result in zip(input_pairs, expected_results):
              self.helper_test_postfix_expr(
                  expr_to_eval=input_pair+SYM_AND,
                  expected_result=expected_result
              )
  
      def test_two_operands_nand(self):
          input_pairs = ["00", "01", "10", "11"]
          expected_results = [1, 1, 1, 0]
          for input_pair, expected_result in zip(input_pairs, expected_results):
              self.helper_test_postfix_expr(
                  expr_to_eval=input_pair+SYM_NAND,
                  expected_result=expected_result
              )
  
      def test_two_operands_or(self):
          input_pairs = ["00", "01", "10", "11"]
          expected_results = [0, 1, 1, 1]
          for input_pair, expected_result in zip(input_pairs, expected_results):
              self.helper_test_postfix_expr(
                  expr_to_eval=input_pair+SYM_OR,
                  expected_result=expected_result
              )
  
      def test_two_operands_nor(self):
          input_pairs = ["00", "01", "10", "11"]
          expected_results = [1, 0, 0, 0]
          for input_pair, expected_result in zip(input_pairs, expected_results):
              self.helper_test_postfix_expr(
                  expr_to_eval=input_pair+SYM_NOR,
                  expected_result=expected_result
              )
  
subject: Add basic tests for evaluate_postfix_expr