def test_nearest_dark_pairs(self):
        """Uses dataset with two dark images, and known relations to the
        science images

        Image info:
        ==

        DARKS
        --
        ./V47_20141104053006639865.fits
        DATE-OBS= '2014-11-04T05:30:06.639865'

        ./V47_20141104054035677809.fits
        DATE-OBS= '2014-11-04T05:40:35.677809'

        SCIENCES
        --
        ./V47_20141104053025349425.fits
        DATE-OBS= '2014-11-04T05:30:25.349425'

        ./V47_20141104053752110943.fits
        DATE-OBS= '2014-11-04T05:37:52.110943'
        """
        test_data_path = path.join(
            __pkg_root__,
            'datasets',
            'tests',
            'ordering_dataset'
        )
        pp = Preprocessor(test_data_path)
        expected = {
            'V47_20141104053025349425': 'V47_20141104053006639865',
            'V47_20141104053752110943': 'V47_20141104054035677809'
        }
        result = pp.nearest_dark_pairings()
        self.assertDictEqual(expected, result)