[TIP] Problem with mock

[John Wong]

I usually mock a class by using autospec parameter so the specs of the
class remains except it's MOCKed.
That allows me to just quickly mock out the class I want while keeping all
the necessary attributes/method I need.

Also, the error doesn't indicate it's a mock object. If it were a mock, I
believe you would see "MagicMock object" rather than DevBuild object.

Just my 2cent. :)

On Wed, Dec 19, 2012 at 3:45 PM, Ken Hagler <khagler at orange-road.com> wrote:

> I've run into a problem using the mock library. It's probably something
> obvious, but I just can't see it. I'm testing this:
>
> def __init__(self, buildNum, configFile = "configfile.txt"):
>         super(DevBuild, self).__init__(buildNum, configFile)
>
>         if configFile == "configfile.txt":
>             self.config.MakeDevBuild()
>
> The superclass's (called Build) __init__ assigns an instance of another
> class (Config) to the self.config attribute. I don't want to run the real
> Build.__init__, so I'm attempting to create a mock object which has a
> config attribute which is another mock, which in turn has a MakeDevBuild
> attribute which is yet another mock.
>
> Here's the best I could come up with:
>
> class TestInit(TestCase):
>     def test_init(self):
>         old_super = __builtin__.super
>
>         mock_Config = MagicMock()
>         mock_Config.MakeDevBuild = MagicMock()
>         mock_Build = MagicMock()
>         mock_Build.config = mock_Config
>         __builtin__.super = mock_Build
>
>         # Test with manual configuration
>         self.testBuild = DevBuild("42", "devconfigfile.txt")
>         self.assertFalse(mock_Config.MakeDevBuild.called)
>
>         # Test with automated configuration
>         self.testBuild = DevBuild("42")
>         mock_Config.MakeDevBuild.assert_called_once_with()
>
>         __builtin__.super = old_super
>
> However, this produces an error:
>
> Error
> Traceback (most recent call last):
>   File "/Users/khagler/Projects/BuildClass/BuildClass/test_devBuild.py",
> line 22, in test_init
>     self.testBuild = DevBuild("42")
>   File "/Users/khagler/Projects/BuildClass/BuildClass/DevBuild.py", line
> 39, in __init__
>     self.config.MakeDevBuild()
> AttributeError: 'DevBuild' object has no attribute 'config'
>
> So I've got as far as getting a mock DevBuild object, but the config
> attribute is missing. Can anyone see what I'm missing?
> --
>                               Ken Hagler
>
> |                   http://www.orange-road.com/                   |
> |   And tho' we are not now that strength which in old days       |
> |   Moved earth and heaven, that which we are, we are --Tennyson  |
>
>
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