code: def test_on_train(self):
      callback = imaging.ImagingCallback()
      mock = MagicMock()
      callback.on_step_training = mock
      callback.process = MagicMock()
      callback = callback.on_train()
      callback.on_step_training("state")
      mock.assert_called_once_with("state")
      callback.process.assert_called_once_with("state")
  
imports: from unittest import TestCase
  from mock import MagicMock, patch, ANY
  import torch
  import torchbearer
  import torchbearer.callbacks.imaging
  import matplotlib.pyplot
label_desc: Use image node_id 8 for calling the TestImagingCallback obj's underlying member method code with example usage: obj.test_on_train() without return types