from mock import patch, Mock
sys.modules['cv2'] = Mock()
from MyClass import MyClass
del sys.modules['cv2']

....

def testFunction()
myObject = MyClass()
self.assertEqual(myObject.val, ?) # here i don't know how to test the equality

import module

val1 = cv2.function(1)
val2 = cv2.function(2)

class MyClass():
 def _init(self)
  self.val = val1