docstr: Test deprecated arg being replaced.
docstr_tok: ["Test","deprecated","arg","being","replaced","."]
code: def test_replacement_arg(self):
      """
      Test deprecated arg being replaced.
      """
  
      @deprecated_arg(
          "b",
          new_name="a",
          since=self.prev_version,
          version_val=self.test_version,
      )
      def afoo4(a, b=None):
          return a
  
      self.assertEqual(afoo4(b=2), 2)
      self.assertEqual(afoo4(1, b=2), 1)  # new name is in use
      self.assertEqual(afoo4(a=1, b=2), 1)
  
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 20 for calling the TestDeprecated obj's underlying member method code with example usage: obj.test_replacement_arg() and returns: a