code: def test_duplicate_flag(self):
      with self.assertRaisesRegex(RuntimeError, "already defined"):
          bool_flag(
              self._flag.name, default=False, help="Another test flag."
          )
  
file_path: flax/tests/configurations_test.py
imports: from unittest import mock
  from absl.testing import absltest
  from flax.configurations import bool_flag, config
label_desc: Use image node_id 2 for calling the MyTestCase obj's underlying member method code with example usage: obj.test_duplicate_flag() without return types