How To Unittest Models With Captcha?

I followed the recipe of ‘Adding CAPTCHA’ on page 126 and now the unittest fails with error.

PHP Fatal error: Call to a member function createAction() on a non-object in yii/framework/validators/CCaptchaValidator.php on line 66

From a design point of view, I prefer the Captcha logic to be in the controller than in the model. The model really has nothing to do with guest or logged in user.

Anyway, how do we unit test models with Captcha?

(or)

How do you avoid Captcha check during unittest?