Python mock patch a function called by another function

Question

def f1():     return 10, True  def f2():     num, stat = f1()     return 2*num, stat 

How do I use python's mock library to patch f1() and return a custom result so I could test f2()?

Edited: Is there something wrong with my test? This doesn't seem to be working, all the tests failed with AssertionError

from foo.bar import f2 from mock import patch  class MyTest(TestCase):      def test_f2_1(self):         with patch('project.module.f1') as some_func:             some_func.return_value = (20, False)             num, stat = f2()             self.assertEqual((num, stat), (40, False))     @patch('project.module.f1')    def test_f2_2(self, some_func):        some_func.return_value = (20, False)        num, stat = f2()        self.assertEqual((num, stat), (40, False)) 

Answer 1

First example suggests that f1() and f2() defined in the same module. Hence the following should work:

from foo.bar import f2 from mock import patch  class MyTest(TestCase):      @patch('foo.bar.f1')     def test_f2_2(self, some_func):         some_func.return_value = (20, False)         num, stat = f2()         self.assertEqual((num, stat), (40, False)) 

Patch is on the same as import: @patch('foo.bar.f1')

Here is a good answer on the issue:

http://bhfsteve.blogspot.nl/2012/06/patching-tip-using-mocks-in-python-unit.html

Answer 2

Assuming that you're using this mock libary:

def f1():     return 10, True  def f2():     num, stat = f1()     return 2*num, stat  import mock  print f2()   # Unchanged f1 -> prints (20, True)  with mock.patch('__main__.f1') as MockClass:       # replace f1 with MockClass      MockClass.return_value = (30, True)     # Change the return value      print f2()     # f2 with changed f1 -> prints (60, True) 

If your code is divided into modules you would probably need to replace __main__.f1 with the path to your module/function.