import unittest
from unittest.mock import patch
 
...
 
class InputHandlerGoodInput(unittest.TestCase):
 
    def setUp(self):
        self.p1 = patch('checkmail.input', create=True)
        self.m1 = self.p1.start()
        self.p2 = patch('getpass.getpass')
        self.m2 = self.p2.start()
  
    def tearDown(self):
        self.p1.stop()
        self.p2.stop()
 
    def test_can_set_default_prompt_for_string_input(self):
        handler = InputHandler()
        handler.start(string_prompt='a')
        handler.input_string()
        handler.end()
        self.m1.assert_called_once_with('a')
 
    ...

 import unittest
class Data(object):
   def add_sub_data(self, sub_data):
      if type(sub_data) != SubData:
         raise Exception('Only SubData need')
      else:
         self.sub_data = sub_data
class SubData(object):
   def __init__(self, param1, param2, param3):
      self.param1 = param1
      self.param2 = param2
      self.param3 = param3
class DataTest(unittest.TestCase):
   def test_add_sub_test(self):
      # Здесь я хотел бы создать мок класса SubData, чтобы в него не надо было передавать param1, param2 и param3

 $stub = $this->getMockBuilder('SubData')->disableOriginalConstructor()->setMethods(array())->getMock();

  
>>> from unittest.mock import Mock
>>> 
>>> m = Mock(spec='abc')
>>> 
>>> isinstance(m, str)
True
>>>