def METHOD_NAME(cubes):
    """Test function ``calculate`` when sic and siconca are available."""
    derived_var = siextent.DerivedVariable()
    out_cube = derived_var.calculate(cubes)
    assert out_cube.units == cf_units.Unit('m2')
    out_data = out_cube.data
    expected = np.ma.ones_like(cubes[0].data)
    expected.mask = True
    expected[0][0][0] = 1.
    np.testing.assert_array_equal(out_data.mask, expected.mask)
    np.testing.assert_array_equal(out_data[0][0][0], expected[0][0][0])