How to use the itkwidgets.trait_types.polydata_list_to_json function in itkwidgets

def test_polydata_list_to_json():
    number_of_points = 10
    point_set_array_1 = np.random.multivariate_normal(gaussian_1_mean, gaussian_1_cov,
                                                      number_of_points)
    point_set_array_2 = np.random.multivariate_normal(gaussian_2_mean, gaussian_2_cov,
                                                      number_of_points)

    point_set_1 = to_point_set(point_set_array_1)
    point_set_2 = to_point_set(point_set_array_2)
    polydata_list = [point_set_1, point_set_2]

    asjson = trait_types.polydata_list_to_json(polydata_list)
    assert(len(asjson) == 2)
    polydata_1 = asjson[0]
    assert(polydata_1['vtkClass'] == 'vtkPolyData')
    assert(polydata_1['points']['vtkClass'] == 'vtkPoints')
    assert(polydata_1['points']['numberOfComponents'] == 3)
    assert(polydata_1['points']['dataType'] == 'Float32Array')
    assert(len(polydata_1['points']['compressedValues']) == 129)

def test_polydata_list_from_json():
    number_of_points = 10
    point_set_array_1 = np.random.multivariate_normal(gaussian_1_mean, gaussian_1_cov,
                                                      number_of_points)
    point_set_array_2 = np.random.multivariate_normal(gaussian_2_mean, gaussian_2_cov,
                                                      number_of_points)

    point_set_1 = to_point_set(point_set_array_1)
    point_set_2 = to_point_set(point_set_array_2)
    polydata_list = [point_set_1, point_set_2]

    asjson = trait_types.polydata_list_to_json(polydata_list)
    polydata_list_from_json = trait_types.polydata_list_from_json(asjson)
    assert(len(polydata_list_from_json) == 2)
    polydata_1 = polydata_list_from_json[0]
    assert(polydata_1['vtkClass'] == 'vtkPolyData')
    assert(polydata_1['points']['vtkClass'] == 'vtkPoints')
    assert(polydata_1['points']['numberOfComponents'] == 3)
    assert(polydata_1['points']['dataType'] == 'Float32Array')
    assert(np.array_equal(polydata_1['points']['values'],
                          point_set_array_1.astype(np.float32)))