'Check results for a single column.'

def check_next_value_results(self, column, results, dates):

    self.assert_result_contains_all_sids(results)
    events = self.raw_events_no_nulls
    dates = dates.tz_localize(None)
    for (asset, asset_result) in results.iteritems():
        relevant_events = events[(events.sid == asset.sid)]
        self.assertEqual(len(relevant_events), 2)
        (v1, v2) = relevant_events[self.next_value_columns[column]]
        (e1, e2) = relevant_events['event_date']
        (t1, t2) = relevant_events['timestamp']
        for (date, computed_value) in zip(dates, asset_result):
            if (t1 <= date <= e1):
                self.assertEqual(computed_value, v1)
            elif (t2 <= date <= e2):
                self.assertEqual(computed_value, v2)
            else:
                assert_equal(computed_value, column.missing_value, allow_datetime_coercions=True)
