def test_extend_frame():
    d = pd.DataFrame({
        'chromo': '1',
        'start': [2, 3, 3, 1, 1],
        'end':   [3, 3, 8, 2, 1]
    })
    d = d.loc[:, ['chromo', 'start', 'end']]
    expect = pd.DataFrame({
        'chromo': '1',
        'start':  [1, 2, 3, 1, 1],
        'end':    [4, 5, 8, 4, 4]
    })
    expect = expect.loc[:, ['chromo', 'start', 'end']]
    actual = annos.extend_len_frame(d, 4)
    npt.assert_array_equal(actual.values, expect.values)