code: def test_parse_foo(self) -> None:
      raw_config = {"union": {"Foo": {"a_param": {"a": 6}}}}
      # pyre-fixme[6]: For 1st param expected `FooUnion` but got `Dict[str,
      #  Dict[str, Dict[str, int]]]`.
      config = Config(**raw_config)
      self.assertEqual(config.union.value.foo(), 12)
  
imports: import abc
  import os
  import unittest
  from reagent.core.configuration import make_config_class, resolve_defaults
  from reagent.core.dataclasses import dataclass, field
  from reagent.core.registry_meta import RegistryMeta
  from reagent.core.tagged_union import TaggedUnion
label_desc: Use image node_id 2 for calling the TestConfigParsing obj's underlying member method code with example usage: obj.test_parse_foo() without return types