code: def test_key_set(self):
      conf = Configuration()
  
      conf.set_string("k1", "v1")
      conf.set_string("k2", "v2")
      conf.set_string("k3", "v3")
      key_set = conf.key_set()
  
      self.assertEqual(key_set, {"k1", "k2", "k3"})
  
file_path: flink/flink-python/pyflink/common/tests/test_configuration.py
imports: from copy import deepcopy
  from pyflink.common import Configuration
  from pyflink.testing.test_case_utils import PyFlinkTestCase
label_desc: Use image node_id 3 for calling the ConfigurationTests obj's underlying member method code with example usage: obj.test_key_set() without return types