def METHOD_NAME(self):
    levels = [0.49, 1.51]
    scheme = 'nearest'
    result = extract_levels(self.cube, levels, scheme)
    expected = np.ma.array([
        [
            [[0., 1.], [2., 3.]],
            [[8., 9.], [10., 11.]],
        ],
        [
            [[12., 13.], [14., 15.]],
            [[20., 21.], [22., 23.]],
        ],
    ])
    self.assert_array_equal(result.data, expected)
    self.shape[self.z_dim] = len(levels)
    self.assertEqual(result.shape, tuple(self.shape))