'If only one ``Snapshot`` is common to the two lists and it appears
somewhere in the middle, it is returned.'

def test_earlier_snapshot_common(self):

    a = Snapshot(name='a')
    b = Snapshot(name='b')
    c = Snapshot(name='c')
    d = Snapshot(name='d')
    e = Snapshot(name='e')
    self.assertEqual(a, _latest_common_snapshot([b, a, c], [d, a, e]))
