How to use the morphio.AnnotationType.single_child function in morphio

(3 -4 0 2)
                      (3 -6 0 2)
                      (3 -8 0 2)
                      (3 -10 0 2)
                      (
                        (3 -10 0 2)
                        (0 -10 0 2)
                        (-3 -10 0 2)
                        |       ; <-- empty sibling but still works !
                       )
                      )
                 ''') as tmp_file:
                n = Morphology(tmp_file.name)
    assert_equal(len(n.annotations), 1)
    annotation = n.annotations[0]
    assert_equal(annotation.type, morphio.AnnotationType.single_child)

assert_substring('It will be merged with the parent section',
                                 err.getvalue().strip())

    assert_equal(len(n.root_sections), 1)
    assert_array_equal(n.root_sections[0].points,
                       np.array([[3, -4, 0],
                                 [3, -6, 0],
                                 [3, -8, 0],
                                 [3, -10, 0],
                                 [0, -10, 0],
                                 [-3, -10, 0]],
                                dtype=np.float32))

    assert_equal(len(n.annotations), 1)
    annotation = n.annotations[0]
    assert_equal(annotation.type, morphio.AnnotationType.single_child)
    assert_equal(annotation.line_number, 6)
    assert_array_equal(annotation.points, [[3, -10, 0], [0, -10, 0], [-3, -10, 0]])
    assert_array_equal(annotation.diameters, [2, 2, 2])