Mock module.function

python_mock.py

############################################################
# how mock really work: just replace the attribute.
############################################################
class MyClass(object):
  def getname(self):
    return 'real getname'

def fake_getname():
  return 'fake getname'

cls = MyClass()
cls.getname = fake_getname
print cls.getname()
cls.getname = Mock(return_value='from mock library')
print cls.getname()





############################################################
# patch module level function
############################################################
i = 1

def GetInfo():
  global i
  i += 1
  return i

def mock_GetInfo():
  global i
  i += 1
  return 2 * i

def PrintInfo():
  print GetInfo()
  print GetInfo()

@patch('__main__.GetInfo')
def testPrintInfo(mock_fn):
  mock_fn.return_value = 1
  mock_fn.side_effect = mock_GetInfo
  PrintInfo()

testPrintInfo()


############################################################
# patch class method.
############################################################

class MyClass(object):

  def getname(self, first, last):
    return first + " " + last

def mock_getname(first, last):
  return "mocked: " + first + " " + last

@patch.object(MyClass, 'getname')
def patched_fn(mock_run):
  mock_run.return_value = 123
  mock_run.side_effect = mock_getname
  cls = MyClass()
  print cls.getname("jianfei", "hu")

patch_fn()



############################################################
# patch entire class.
############################################################

@patch('__main__.MyClass')
def patched_cls(mock_cls):
  # mock_run = MagicMock()
  # #mock_run.side_effect = fake_showrun
  # mock_run.return_value = 12345
  # mocked_cls.showrun = mock_run
  mock_op = MagicMock(return_value="always same")
  mock_op.return_value = "always same" # class name will be called and treated as function in eyes of Mock()
  mock_instance = MagicMock()
  mock_instance.getname = mock_op

  mock_cls.return_value = mock_instance
  
  cls = MyClass()
  print cls.getname("jianfei", "hu")