'The MX record with the lowest preference is returned by
L{MXCalculator.getMX}.'

def test_mailExchangePreference(self):

    domain = 'example.com'
    good = 'good.example.com'
    bad = 'bad.example.com'
    records = [RRHeader(name=domain, type=Record_MX.TYPE, payload=Record_MX(1, bad)), RRHeader(name=domain, type=Record_MX.TYPE, payload=Record_MX(0, good)), RRHeader(name=domain, type=Record_MX.TYPE, payload=Record_MX(2, bad))]
    return self._exchangeTest(domain, records, good)
