'Acquiring a lease on node A if a lease already exits for that dataset
on node A will override the timeout.'

def test_renew(self):

    self.clock.advance(self.now)
    expires = 40
    expected_expiration = datetime.fromtimestamp((self.clock.seconds() + expires), UTC)
    d = self.acquire_lease(None)
    d.addCallback((lambda _: self.acquire_lease(expires, OK)))
    def acquired(_):
        self.assertEqual(self.persistence_service.get().leases[self.dataset3], Lease(dataset_id=self.dataset3, node_id=self.node3, expiration=expected_expiration))
    d.addCallback(acquired)
    return d
