docstr: StreamQuery - StateManager - keys
docstr_tok: ["StreamQuery","-","StateManager","-","keys"]
code: def test_keys(self):
      """StreamQuery - StateManager - keys"""
      self._state_manager.set("aaa", "bbbbb")
      self._state_manager.set("ccc", "ddddd")
  
      assert_equals(self._state_manager.keys, ["aaa", "ccc"])
  
file_path: streamalert/tests/unit/streamalert/scheduled_queries/state/test_state_manager.py
imports: from datetime import datetime
  from mock import MagicMock
  from nose.tools import assert_equals, assert_true, assert_false
  from streamalert.scheduled_queries.state.state_manager import StateManager, StepFunctionStateManager
label_desc: Use image node_id 4 for calling the TestStateManager obj's underlying member method code with example usage: obj.test_keys() without return types