[openstack-dev] [all][code quality] Voting coverage job (-1 if coverage get worse after patch)

Sean Dague sean at dague.net
Mon Apr 20 11:13:31 UTC 2015

On 04/18/2015 09:30 PM, Boris Pavlovic wrote:
> Hi stackers, 
> Code coverage is one of the very important metric of overall code
> quality especially in case of Python. It's quite important to ensure
> that code is covered fully with well written unit tests. 
> One of the nice thing is coverage job. 
> In Rally we are running it against every check which allows us to get
> detailed information about
> coverage before merging patch: 
> http://logs.openstack.org/84/175084/1/check/rally-coverage/c61d5e1/cover/
> This helped Rally core team to automate checking that new/changed code
> is covered by unit tests and we raised unit test coverage from ~78% to
> almost 91%. 
> But it produces few issues: 
> 1) >9k nitpicking - core reviewers have to put -1 if something is not
> covered by unit tests
> 2) core team scaling issues - core team members spend a lot of time just
> checking that whole code is covered by unit test and leaving messages
> like this should be covered by unit test 
> 3) not friendly community - it's not nice to get on your code -1 from
> somebody that is asking just to write unit tests
> 4) coverage regressions - sometimes we accidentally accept patches that
> reduce coverage  
> To resolve this issue I improved a bit coverage job in Rally project,
> and now it compares master vs master + patch coverage. If new coverage
> is less than master job is marked as -1. 
> Here is the patch for job enhancement: 
> https://review.openstack.org/#/c/174645/
> Here is coverage job in action:
> patch https://review.openstack.org/#/c/174677/
> job message
> http://logs.openstack.org/77/174677/4/check/rally-coverage/ba49c90/console.html#_2015-04-17_15_57_17_695

Honestly, I'm suspicious of approaches like this. While 90% coverage is
clearly better than 0% coverage, it's not clear that 91% coverage is
always better than 90% coverage. Especially when you talk about larger
and more complex code bases.

I actually firmly feel that #3 is wrong. I think it's a lot better to
have an early conversation with people about unit tests that need to be
written when they don't submit any. Because I think it's a lot less
friendly to have someone iterate 10 patches to figure out how to pass a
bot's idea of good tests, and then have a reviewer say it's wrong.

Honestly, coverage for projects seems to me to be more of an analog
measure that would be good to graph over time and make sure it's not
regression, but personally I think the brownian motion of individual
patches seems like it's not a great idea to gate on every single patch.
I personally would be -1 for adding this to projects that I have +2 on.


Sean Dague

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