code: def testStringFormat(self):
      mask = field_mask_pb2.FieldMask()
      self.assertEqual("", mask.ToJsonString())
      mask.paths.append("foo")
      self.assertEqual("foo", mask.ToJsonString())
      mask.paths.append("bar")
      self.assertEqual("foo,bar", mask.ToJsonString())
  
      mask.FromJsonString("")
      self.assertEqual("", mask.ToJsonString())
      mask.FromJsonString("foo")
      self.assertEqual(["foo"], mask.paths)
      mask.FromJsonString("foo,bar")
      self.assertEqual(["foo", "bar"], mask.paths)
  
      # Test camel case
      mask.Clear()
      mask.paths.append("foo_bar")
      self.assertEqual("fooBar", mask.ToJsonString())
      mask.paths.append("bar_quz")
      self.assertEqual("fooBar,barQuz", mask.ToJsonString())
  
      mask.FromJsonString("")
      self.assertEqual("", mask.ToJsonString())
      mask.FromJsonString("fooBar")
      self.assertEqual(["foo_bar"], mask.paths)
      mask.FromJsonString("fooBar,barQuz")
      self.assertEqual(["foo_bar", "bar_quz"], mask.paths)
  
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 1 for calling the FieldMaskTest obj's underlying member method code with example usage: obj.testStringFormat() without return types