Trouble patching a function of a function

Question

I'm pretty new to patching and I've run into a something I don't know how to patch. Basically, in the file I want to test, there is the method difficult_method(). It looks a little like this:

from import_location import User

def difficult_method():
  ids = list_of_ids
  for id in list_of_ids:
    try:
      user = User.query.filter(User.id == user_id).all()[0]
    except:
      continue
    #do lots of stuff

The code I want to mock is User.query.filter(User.id == user_id).all() and as far as I am concerned it can return a static list. How would I replace that line in code that looks something like this:

from mock import patch

@patch(#what would go here?)
def test_difficult_method(): 
  from file_to_test import difficult_method
  assert difficult_method() returns ...

Answer 1

I figured it out! The key was to create a MockUser class, like so:

user = #creating a user

class MockFilter(object):
  def all(self):
    return [user]


class MockQuery(object):

  def filter(self, match):
    return MockFilter()


class MockUser(object):
  query = MockQuery()
  id = '2'

Then I patched it in like so:

from mock import patch

@patch('import_location.User', MockUser)
def test_difficult_method(): 
  from file_to_test import difficult_method
  assert difficult_method() returns ...