Q:

Python: Problems mocking an instance

I am having problem mocking an object to test a descriptor.
This is the code of the descriptor:
class Text(object):
    def __init__(self, default_value=u'', validators=[]):
        self.validators = validators
        self._value = default_value

    def __set__(self, instance, value):
         for validator in self.validators:
               validator(value).validate()

this is the test:
def test_text_validator_raises_exception(self):
   validator = Mock()
   validator.validate.side_effect = ValidationError()
   text = Text(validators=[validator])
   self.assertRaises( ValidationError, text__set__, (text, '') )

Edit:
The function has () in the code I did a typo when copying the code.
The error I got was that set() takes exactly 3 arguments. But I noticed in the answers that I shouldn't pass a tuple as a last argument.
But It also isn't working when I called validator('').validate() inside the test function.

A:

validator in Text is an object factory e.g., class object
validator in the test_.. function is used as a concrete instance -- the product of an object factory. 

You should give to Text() something that returns objects with .validate method not the objects themselves:
def test_text_validator_raises_exception(self):
    validator = Mock()
    validator.validate.side_effect = ValidationError()
    text = Text(validators=[Mock(return_value=validator)])
    self.assertRaises(ValidationError, text.__set__, text, '')

