code: def test_forward_compatible_arguments_real_use_case(self):
      # this change introduced forward incompatibility in the past
      old_slice_schema = parse_schema(
          "slice(Tensor(a) self, int dim=0, int start=0, int end=0, int step=1) -> Tensor(a)"
      )
      new_slice_schema = parse_schema(
          "slice(Tensor(a) self, int dim=0, int? start=None, int? end=None, int step=1) -> Tensor(a)"
      )
      is_fc, reason = new_slice_schema.check_forward_compatible_with(
          old_slice_schema
      )
      self.assertFalse(is_fc)
      self.assertEqual(
          reason,
          "'start' is not forward compatible with the older version of the schema",
      )
  
file_path: pytorch/test/test_function_schema.py
imports: import torch
  from torch.testing._internal.common_utils import TestCase, run_tests
  from torch._C import parse_schema
label_desc: Use image node_id 10 for calling the TestFunctionSchema obj's underlying member method code with example usage: obj.test_forward_compatible_arguments_real_use_case() without return types