How can one mock/stub python module like urllib

Question

I need to test a function that needs to query a page on an external server using urllib.urlopen (it also uses urllib.urlencode). The server could be down, the page could cha

Answer 1

The simplest way is to change your function so that it doesn't necessarily use urllib.urlopen. Let's say this is your original function:

def my_grabber(arg1, arg2, arg3):
    # .. do some stuff ..
    url = make_url_somehow()
    data = urllib.urlopen(url)
    # .. do something with data ..
    return answer

Add an argument which is the function to use to open the URL. Then you can provide a mock function to do whatever you need:

def my_grabber(arg1, arg2, arg3, urlopen=urllib.urlopen):
    # .. do some stuff ..
    url = make_url_somehow()
    data = urlopen(url)
    # .. do something with data ..
    return answer

def test_my_grabber():
    my_grabber(arg1, arg2, arg3, urlopen=my_mock_open)