Mocking, Python

I have used Python mock and patch to do some testing for the OPTIONS call and also the server type check in Swift. unittest.mock is a library for testing in Python. It can be used to replace parts of the code, return data and then make assertions about them.

class unittest.mock.Mock(side_effect=None, return_value=DEFAULT, **kwargs)

side_effect: A function to be called whenever the Mock is called. It is useful to raise exceptions.
return_value: The value returned when the mock is called.

Mock provides a patching module that could be used to patch a specific function, class, class level attributes in the scope of test. For instance,

@mock.patch(‘eventlet.green.urllib2.urlopen’)
def test_foo(self, mock_urlopen):
def getheader(name):
d = {‘Server’: ‘server-type’}
return d.get(name)
mock_urlopen.return_value.info.return_value.getheader = getheader

In the above function that I used a mock patch to mock urlopen and it’s return value. To test the OPTIONS call in swift-recon, this simulation will faciliate me by returning header value of “Server” as “server-type”. Further, I could assert the return of the actual value returned by the scout_server_type method in recon (which calls OPTIONS), like this:

self.assertEqual(content, ‘server-type’)

Content here is the return value of OPTIONS call in recon.py.

To test the validate servers method (server_type_check) call, I could have created a fake class for scout_server_type or mock the method itself. I have done the latter:

def mock_scout_server_type(app, host):
url = ‘http://%s:%s/’ % (host[0], host[1])
response = responses[host[1]]
status = 200
return url, response, status

patches = [
mock.patch(‘swift.cli.recon.Scout.scout_server_type’,
mock_scout_server_type),
mock.patch(‘sys.stdout’, new=stdout),
]

This mock, will allow me to replace the scout_server_type call and instead call “mock_scout_server_type” and returns those method’s values for the scope of the test.

with nested(*patches):
self.recon.server_type_check(hosts)

With the above, when server_type_check is called, the internal call to scout_server_type will be replaced by mock_scout_server_type.