def ascii_escaped(val: bytes | str) -> str:
    r"""If val is pure ASCII, return it as an str, otherwise, escape
    bytes objects into a sequence of escaped bytes:

    b'\xc3\xb4\xc5\xd6' -> r'\xc3\xb4\xc5\xd6'

    and escapes strings into a sequence of escaped unicode ids, e.g.:

    r'4\nV\U00043efa\x0eMXWB\x1e\u3028\u15fd\xcd\U0007d944'

    Note:
       The obvious "v.decode('unicode-escape')" will return
       valid UTF-8 unicode if it finds them in bytes, but we
       want to return escaped bytes for any byte, even if they match
       a UTF-8 string.
    """
    if isinstance(val, bytes):
        ret = val.decode("ascii", "backslashreplace")
    else:
        ret = val.encode("unicode_escape").decode("ascii")
    return ret.translate(_non_printable_ascii_translate_table)
If val is pure ASCII, return it as an str, otherwise, escape
    bytes objects into a sequence of escaped bytes:

    b'\xc3\xb4\xc5\xd6' -> r'\xc3\xb4\xc5\xd6'

    and escapes strings into a sequence of escaped unicode ids, e.g.:

    r'4\nV\U00043efa\x0eMXWB\x1e\u3028\u15fd\xcd\U0007d944'

    Note:
       The obvious "v.decode('unicode-escape')" will return
       valid UTF-8 unicode if it finds them in bytes, but we
       want to return escaped bytes for any byte, even if they match
       a UTF-8 string.
    
src/_pytest/compat.py