[openstack-dev] [nova] Do we have some guidelines for mock, stub, mox when writing unit test?

Russell Bryant rbryant at redhat.com
Wed Dec 4 17:10:14 UTC 2013

On 12/04/2013 11:16 AM, Nikola Đipanov wrote:
> Resurrecting this thread because of an interesting review that came up
> yesterday [1].
> It seems that our lack of a firm decision on what to do with the mocking
> framework has left people confused. In hope to help - I'll give my view
> of where things are now and what we should do going forward, and
> hopefully we'll reach some consensus on this.
> Here's the breakdown:
> We should abandon mox:
> * It has not had a release in over 3 years [2] and a patch upstream for 2
> * There are bugs that are impacting the project with it (see above)
> * It will not be ported to python 3
> Proposed path forward options:
> 1) Port nova to mock now:
>   * Literally unmanageable - huge review overhead and regression risk
> for not so much gain (maybe) [1]
> 2) Opportunistically port nova (write new tests using mock, when fixing
> tests, move them to mock):
>  * Will take a really long time to move to mock, and is not really a
> solution since we are stuck with mock for an undetermined period of time
> - it's what we are doing now (kind of).
> 3) Same as 2) but move current codebase to mox3
>  * Buys us py3k compat, and fresher code
>  * Mox3 and mox have diverged and we would need to backport mox fixes
> onto the mox3 three and become de-facto active maintainers (as per Peter
> Feiner's last email - that may not be so easy).
> I think we should follow path 3) if we can, but we need to:
> 1) Figure out what is the deal with mox3 and decide if owning it will
> really be less trouble than porting nova. To be hones - I was unable to
> even find the code repo for it, only [3]. If anyone has more info -
> please weigh in. We'll also need volunteers
> 2) Make better testing guidelines when using mock, and maybe add some
> testing helpers (like we do already have for mox) that will make porting
> existing tests easier. mreidem already put this on this weeks nova
> meeting agenda - so that might be a good place to discuss all the issues
> mentioned here as well.
> We should really take a stronger stance on this soon IMHO, as this comes
> up with literally every commit.

I think option 3 makes the most sense here (pending anyone saying we
should run away screaming from mox3 for some reason).  It's actually
what I had been assuming since this thread a while back.

This means that we don't need to *require* that tests get converted if
you're changing one.  It just gets you bonus imaginary internet points.

Requiring mock for new tests seems fine.  We can grant exceptions in
specific cases if necessary.  In general, we should be using mock for
new tests.

Russell Bryant

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