[Python-ideas] SealedMock proposal for unittest.mock

Victor Stinner victor.stinner at gmail.com
Thu Jun 1 08:17:05 EDT 2017

A stricter mock object cannot be a bad idea :-) I am not sure about your
proposed API: some random code may already use this attribute. Maybe it can
be a seal (mock) function which sets a secret attribute with a less common

Yeah, please open an issue on bugs.python.org ;-)


Le 29 mai 2017 11:33 PM, "Mario Corchero" <mariocj89 at gmail.com> a écrit :

> Hello Everyone!
> First time writing to python-ideas.
> *Overview*
> Add a new mock class within the mock module
> <https://github.com/python/cpython/blob/master/Lib/unittest/mock.py>,
> SealedMock (or RestrictedMock) that allows to restrict in a dynamic and
> recursive way the addition of attributes to it. The new class just defines
> a special attribute "sealed" which once set to True the behaviour of
> automatically creating mocks is blocked, as well as for all its "submocks".
> See sealedmock
> <https://github.com/mariocj89/sealedmock/blob/master/README.md>. Don't
> focus on the implementation, it is ugly, it would be much simpler within
> *mock.py*.
> *Rationale*
> Inspired by GMock
> <https://github.com/google/googletest/tree/master/googlemock> RestrictedMock,
> SealedMock aims to allow the developer to define a narrow interface to the
> mock that defines what the mocks allows to be called on.
> The feature of mocks returning mocks by default is extremely useful but
> not always desired. Quite often you rely on it only at the time you are
> writing the test but you want it to be disabled at the time the mock is
> passed into your code, that is what SealedMock aims to address.
> This solution also prevents user errors when mocking incorrect paths or
> having typos when calling attributes/methods of the mock.
> We have tried it internally in our company and it gives quite a nicer user
> experience for many use cases, specially for new users of mock as it helps
> out when you mock the wrong path.
> *Alternatives*
>    - Using auto_spec/spec is a possible solution but removes flexibility
>    and is rather painful to write for each of the mocks and submocks being
>    used.
>    - Leaving it outside of the mock.py as it is not interesting enough. I
>    am fine with it :) just proposing it in case you think otherwise.
>    - Make it part of the standard Mock base class. Works for me, but I'd
>    concerned on how can we do it in a backward compatible way. (Say someone is
>    mocking something that has a "sealed" attribute already).
> Let me know what you think, happy to open a enhancement in
> https://bugs.python.org/ and send a PR.
> Regards,
> Mario
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