code: def test_on_val(self):
      callback = imaging.ImagingCallback()
      mock = MagicMock()
      callback.on_step_validation = mock
      callback.process = MagicMock()
      callback = callback.on_val()
      state = {torchbearer.DATA: torchbearer.TEST_DATA}
      callback.on_step_validation(state)
      mock.assert_called_once_with(state)
      self.assertTrue(callback.process.call_count == 0)
  
      mock.reset_mock()
      callback.process.reset_mock()
  
      state = {torchbearer.DATA: torchbearer.VALIDATION_DATA}
      callback.on_step_validation(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 9 for calling the TestImagingCallback obj's underlying member method code with example usage: obj.test_on_val() without return types