code: def testCamelCaseToSnakeCase(self):
      self.assertEqual(
          "foo_bar", well_known_types._CamelCaseToSnakeCase("fooBar")
      )
      self.assertEqual(
          "_foo_bar", well_known_types._CamelCaseToSnakeCase("FooBar")
      )
      self.assertEqual(
          "foo3_bar", well_known_types._CamelCaseToSnakeCase("foo3Bar")
      )
      self.assertRaisesRegexp(
          well_known_types.ParseError,
          'Fail to parse FieldMask: Path name foo_bar must not contain "_"s.',
          well_known_types._CamelCaseToSnakeCase,
          "foo_bar",
      )
  
imports: from datetime import datetime
  from google.protobuf import any_pb2
  from google.protobuf import duration_pb2
  from google.protobuf import field_mask_pb2
  from google.protobuf import struct_pb2
  from google.protobuf import timestamp_pb2
  from google.protobuf import unittest_pb2
  from google.protobuf.internal import any_test_pb2
  from google.protobuf.internal import test_util
  from google.protobuf.internal import well_known_types
  from google.protobuf import descriptor
  from google.protobuf import text_format
label_desc: Use image node_id 8 for calling the FieldMaskTest obj's underlying member method code with example usage: obj.testCamelCaseToSnakeCase() without return types