router not routing

gistfile1.py

$ cat ztest1.py
import time
import zmq

ctx = zmq.Context()

req_sock = ctx.socket(zmq.REQ)
req_sock.connect('ipc://req-test')

router_sock = ctx.socket(zmq.ROUTER)
router_sock.setsockopt(zmq.ROUTER_MANDATORY, 1)
router_sock.connect('ipc://router-test')

while True:
        print 'querying for id'
        req_sock.send('get')
        id = req_sock.recv()
        print 'id is %s. sending message via router' % id
        try:
                router_sock.send_multipart([id, '', 'hello'])
        except zmq.error.ZMQError as e:
                print 'failed to send via router: %s' % e
        time.sleep(2)


$ cat ztest2.py
import time
import uuid
import zmq

ctx = zmq.Context()

instance_id = str(uuid.uuid4())

rep_sock = ctx.socket(zmq.REP)
rep_sock.bind('ipc://req-test')

router_sock = ctx.socket(zmq.ROUTER)
router_sock.identity = instance_id
router_sock.bind('ipc://router-test')

poller = zmq.Poller()
poller.register(rep_sock, zmq.POLLIN)
poller.register(router_sock, zmq.POLLIN)

while True:
        socks = dict(poller.poll())
        if socks.get(rep_sock) == zmq.POLLIN:
                rep_sock.recv()
                print 'responding to query for id'
                rep_sock.send(instance_id)
        elif socks.get(router_sock) == zmq.POLLIN:
                print router_sock.recv_multipart()