worker.py

#!/usr/bin/env python
import urllib

class Worker(object):

    def __init__(self, myurl):
        self.myurl = myurl

    def dowork(self):
        resp = urllib.request.urlopen(self.myurl)
        print(resp.read())

worker_test.py

#!/usr/bin/env python
import nose, unittest
from unittest import mock
from unittest.mock import patch

from worker import Worker

class WorkerTest(unittest.TestCase):
    def setUp(self):
        self.wrkr = Worker('http://www.234234ljk.com')
        return

    @patch('worker.urllib.request.urlopen', auto_spec=True)
    def dowork_test(self, urlopen):
        myobj = mock.Mock()
        myobj.read.return_value = "This was successfully mocked."

        urlopen.return_value = myobj
        self.wrkr.dowork()
        assert True == myobj.read.called 

if '__main__' == __name__:
    nose.main() # nose is so cool