code: def test_external_diagonal(self, xp, dtype):
      a = testing.shaped_arange((3, 4, 5), xp, dtype)
      return xp.diagonal(a, 1, 2, 0)
  
imports: import unittest
  import numpy
  import pytest
  import cupy
  from cupy import testing
label_desc: Use image node_id 16 for calling the TestIndexing obj's underlying member method code with example usage: obj.test_external_diagonal(xp, dtype) and returns: xp