code: def test_on_sample(self, mock_torch):
      mock_torch.randperm.return_value = torch.Tensor(
          [3, 2, 1, 0]
      ).long()
      callback = SamplePairing(
          policy=SamplePairing.default_policy(0, 10, 10, 10)
      )
  
      state = {
          torchbearer.INPUT: torch.Tensor([0.25, 0.5, 0.75, 1]),
          torchbearer.EPOCH: 0,
      }
      callback.on_sample(state)
      self.assertTrue(
          ((state[torchbearer.INPUT] - 0.625).abs() < 0.0001).all()
      )
  
file_path: torchbearer/tests/callbacks/test_sample_pairing.py
imports: from unittest import TestCase
  from mock import patch, call
  import torch
  import torchbearer
  from torchbearer.callbacks import SamplePairing
label_desc: Use image node_id 1 for calling the TestSamplePairing obj's underlying member method code with example usage: obj.test_on_sample(mock_torch) without return types