code: def test_amp_precision_backward():
      precision = MixedPrecision(precision="16-mixed", device="cuda")
      precision.scaler = Mock()
      precision.scaler.scale = Mock(side_effect=(lambda x: x))
      tensor = Mock()
      model = Mock()
      precision.backward(tensor, model, "positional-arg", keyword="arg")
      precision.scaler.scale.assert_called_once_with(tensor)
      tensor.backward.assert_called_once_with(
          "positional-arg", keyword="arg"
      )
  
file_path: pytorch-lightning/tests/tests_fabric/plugins/precision/test_amp.py
imports: import re
  from unittest.mock import Mock
  import pytest
  import torch
  from lightning.fabric.plugins.precision.amp import MixedPrecision
label_desc: Use image node_id 4 for calling a global function with example usage: test_amp_precision_backward() without return types