Python: Problems mocking an instance

Question

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.

Sorry, should have been more clear.

Pickels
– Pickels

2010-11-12 22:35:16 +00:00
Commented Nov 12, 2010 at 22:35 — Pickels
– Pickels, Commented Nov 12, 2010 at 22:35

jfs · Accepted Answer · 2010-11-12 20:07:10Z

3

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, '')

answered Nov 12, 2010 at 20:07

jfs

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3 Comments

Pickels Over a year ago

This is actually what I was trying to ask. Was trying to figure out how to let mock return a class instead of an object. In your example doesn't Mock(return_value=validator) also return the instance of the object instead of class?

Pickels Over a year ago

Tried it and it works, thanks a lot. Going to try and not make any questions anymore when I am in a hurry since it all got a little messy. Thanks again.

jfs Over a year ago

@Pickels: Consider: f = Mock(return_value=validator). Here's f is an object that returns validator when you call it e.g., f(value) == validator. f and f() are different things in Python.

Asterisk · Accepted Answer · 2010-11-12 19:50:17Z

1

I guess you need to put () after function name

answered Nov 12, 2010 at 19:50

Asterisk

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1 Comment

Constantin Over a year ago

Yes, def test_text_validator_raises_exception certainly needs ().

Jough Dempsey · Accepted Answer · 2010-11-12 20:07:36Z

0

Maybe the best way to mock an instance is just "You call yourself an instance?"

Seriously, though, def test_text_validator_raises_exception: should be def test_text_validator_raises_exception():

But what problem are you having with it, as the first commenter asked?

answered Nov 12, 2010 at 20:07

Jough Dempsey

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