code: def test_operate_4d_array(self):
      a = np.zeros((3, 3, 3, 3), int)
      fill_diagonal(a, 4)
      i = np.array([0, 1, 2])
      assert_equal(np.where(a != 0), (i, i, i, i))
  
imports: import pytest
  import numpy
  from numpy.testing import assert_, assert_equal, assert_array_equal, assert_almost_equal, assert_array_almost_equal, assert_raises, assert_raises_regex
  from numpy.lib._index_tricks_impl import mgrid, ogrid, ndenumerate, fill_diagonal, diag_indices, diag_indices_from, index_exp, ndindex, c_, r_, s_, ix_
label_desc: Use image node_id 5 for calling the TestFillDiagonal obj's underlying member method code with example usage: obj.test_operate_4d_array() without return types