code: def test_multi(self):
      def example(state):
          return state
  
      state = "test"
      c = callbacks.on_backward(
          callbacks.on_sample(callbacks.on_start(example))
      )
      self.assertTrue(c.on_backward(state) == state)
      self.assertTrue(c.on_sample(state) == state)
      self.assertTrue(c.on_start(state) == state)
  
imports: import unittest
  import torchbearer.callbacks
  import torchbearer
label_desc: Use image node_id 1 for calling the TestDecorators obj's underlying member method code with example usage: obj.test_multi() and returns: state