code: def test_backslash_not_treated_specially() -> None:
      r"""When generating nodeids, if the source name contains special characters
      like a newline, they are escaped into two characters like \n. Therefore, a
      user will never need to insert a literal newline, only \n (two chars). So
      mark expressions themselves do not support escaping, instead they treat
      backslashes as regular identifier characters."""
      matcher = {r"\nfoo\n"}.__contains__
  
      assert evaluate(r"\nfoo\n", matcher)
      assert not evaluate(r"foo", matcher)
      with pytest.raises(ParseError):
          evaluate("\nfoo\n", matcher)
  
file_path: pytest/testing/test_mark_expression.py
imports: from typing import Callable
  import pytest
  from _pytest.mark.expression import Expression
  from _pytest.mark.expression import ParseError
label_desc: Use image node_id 5 for calling a global function with example usage: test_backslash_not_treated_specially() without return types