code: def test_diag(self):
      x = np.zeros((3, 3, 3), int)
      x[0, 2, 2] = 1
      x[1, 1, 1] = 1
      x[2, 0, 0] = 1
      assert_array_equal(label(x), x)
  
imports: import numpy
  from skimage.measure import label
  import skimage.measure._ccomp
  from skimage._shared import testing
  from skimage._shared.testing import assert_array_equal
label_desc: Use image node_id 4 for calling the TestConnectedComponents3d obj's underlying member method code with example usage: obj.test_diag() without return types