docstr: Test deprecated_arg decorator raises exception with `removed` set in the past.
  with unknown version
docstr_tok: ["Test","deprecated_arg","decorator","raises","exception","with","`","removed","`","set","in","the","past",".","with","unknown","version"]
code: def test_arg_except2_unknown(self):
      """
      Test deprecated_arg decorator raises exception with `removed` set in the past.
      with unknown version
      """
  
      @deprecated_arg(
          "b",
          removed=self.prev_version,
          version_val="0+untagged.1.g3131155",
      )
      def afoo4(a, b=None):
          pass
  
      afoo4(1, b=2)
  
imports: from __future__ import annotations
  import unittest
  import warnings
  from monai.utils import DeprecatedError, deprecated, deprecated_arg, deprecated_arg_default
label_desc: Use image node_id 18 for calling the TestDeprecated obj's underlying member method code with example usage: obj.test_arg_except2_unknown() without return types