code: def test_diag_extraction_from_nested_list(self, xp):
      a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
      r = xp.diag(a, 1)
      assert isinstance(r, xp.ndarray)
      return r
  
imports: import unittest
  import numpy
  import pytest
  import cupy
  from cupy import testing
label_desc: Use image node_id 4 for calling the TestMatrix obj's underlying member method code with example usage: obj.test_diag_extraction_from_nested_list(xp) and returns: r