code: def test_return_num(self):
      x = np.array([[1, 0, 6], [0, 0, 6], [5, 5, 5]])
  
      assert_array_equal(label(x, return_num=True)[1], 3)
      assert_array_equal(label(x, background=-1, return_num=True)[1], 4)
  
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 10 for calling the TestConnectedComponents3d obj's underlying member method code with example usage: obj.test_return_num() without return types