'An acquired lease expires after the specified number of seconds and
is removed from the ``Leases`` map.'

def test_lease_expires(self):

    leases = self.leases.acquire(self.now, self.dataset_id, self.node_id, self.lease_duration)
    self.assertIn(self.dataset_id, leases)
    now = (self.now + datetime.timedelta(seconds=(self.lease_duration + 1)))
    leases = leases.expire(now)
    self.assertNotIn(self.dataset_id, leases)
