Python - Monkey Patching weird bug

Question

My Fake Mock Class looks like following:

class FakeResponse:
 method = None # 
 url = None # static class variables
 def __init__(self, method, url, data):#, response):
 self.status_code = 200 # always return 200 OK
 FakeResponse.method = method # 
 FakeResponse.url = url #
 @staticmethod
 def check(method, url, values):
 """ checks method and URL. 
 """
 print "url fake: ", FakeResponse.url
 assert FakeResponse.method == method
 assert FakeResponse.url == url

I have another decorator which is applicable over all the test cases:

@pytest.fixture(autouse=True)
def no_requests(monkeypatch):
 monkeypatch.setattr('haas.cli.do_put',
 lambda url,data: FakeResponse('PUT', url, data))
 monkeypatch.setattr("haas.cli.do_post",
 lambda url,data: FakeResponse('POST', url, data))
 monkeypatch.setattr("haas.cli.do_delete",
 lambda url: FakeResponse('DELETE', url, None))

I am using Py.test to test the code.

Some example test cases are:

class Test:
 #test case passes
 def test_node_connect_network(self):
 cli.node_connect_network('node-99','eth0','hammernet')
 FakeResponse.check('POST','http://abc:5000/node/node-99/nic/eth0/connect_network',
 {'network':'hammernet'})
 # test case fails
 def test_port_register(self):
 cli.port_register('1') # This make a indirect REST call to the original API
 FakeResponse.check('PUT','http://abc:5000/port/1', None)
 # test case fails
 def test_port_delete(self):
 cli.port_delete('port', 1)
 FakeResponse.check('DELETE','http://abc:5000/port/1', None) 

A sample error message which I get:

 method = 'PUT', url = 'http://abc:5000/port/1', values = None
 @staticmethod
 def check(method, url, values):
 """ checks method and URL.
 'values': if None, verifies no data was sent.
 if list of (name,value) pairs, verifies that each pair is in 'values'
 """
 print "url fake: ", FakeResponse.url
> assert FakeResponse.method == method
E assert 'POST' == 'PUT'
E - POST
E + PUT
haas/tests/unit/cli_v1.py:54: AssertionError
--------------------------------------------- Captured stdout call -------------------------------------
port_register <port>
Register a <port> on a switch
url fake: http://abc:5000/node/node-99/nic/eth0/connect_network
--------------------------------------------- Captured stderr call -------------------------------------
Wrong number of arguements. Usage: 

Whereas if I call the second test case in the following way considering the check function takes "self" argument and @staticmethod is not used then the test case works:

def test_port_register(self):
 cli.port_register('1')
 fp = FakeResponse('PUT','http://abc:5000/port/1', None) #Create a FakeResponse class instance
 fp.check('PUT','http://abc:5000/port/1', None) # Just call the check function with the same 
 arguments

Questions:

• Are there any side effects of using monkey patching and @staticmethod
• How is the url defined for a previous test function being used in the next function call.
• Should'nt there be a scoping of argument to disallow the above unwanted behavior.
• Is there a better way to monkey patch.

Sorry for the long post, I have been trying to resolve this for a week and wanted some perspective of other programmers.

• Daniel Roseman: It's not clear what you are expecting to happen here. You're explicitly using class attributes, so I don't see why you're surprised when they persist between instances: that's the whole point of class attributes.
• abhi09: Is there a better way to accomplish the fake test. Internally the attributes of FakeResponse class are used in another module to do some computation.
• Michele d'Amico: Try to debug cli.port_register('1') and check it not call a POST request after the PUT. Your code is not beautiful but it should work... but only check last call to FakeResponse()
• Michele d'Amico: You can try to use mock framework to build a mock request. I can try to fill an answer later by using mock framework.

Answer 1

The issue was not having the right signature for one of the functions. It was resolved by changing the argument passed to the MonkeyPatch function as en empty dictionary {} instead of 'None' value which is kind of specific to my code.

The reason the I was initially hitting the issue was, as the current function's call(cli.port_register) was failing when the parameters where passed to port_register itself, so it picked up the argument values from a previous state and doing the assert with the FakeResponse call.