code: def test_contains(self):
      s = State()
  
      key1 = torchbearer.state_key("test_a")
      key2 = torchbearer.state_key("test_b")
  
      s[key1] = 1
      s[key2] = 2
  
      self.assertTrue(s.__contains__(key1))
  
imports: import unittest
  import warnings
  import torchbearer
  from torchbearer.state import State
label_desc: Use image node_id 1 for calling the TestState obj's underlying member method code with example usage: obj.test_contains() without return types