code: def test_main(self):
      callback = imaging.CachingImagingCallback(
          key="my_key", num_images=5
      )
      self.assertRaises(
          NotImplementedError, lambda: callback.on_cache("", {})
      )
  
      callback.on_cache = MagicMock()
      callback.on_cache.return_value = "image"
  
      state = {"my_key": torch.ones(10, 3, 2, 2), torchbearer.BATCH: 0}
      callback.on_batch(state)
      self.assertTrue(callback.on_cache.call_args[0][0].sum() == 60)
      self.assertTrue(callback.on_cache.call_args[0][1] == 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 1 for calling the TestCachingImagingCallback obj's underlying member method code with example usage: obj.test_main() without return types