[openstack-dev] Proposal for including fake implementations in python-client packages

Christopher Armstrong chris.armstrong at rackspace.com
Wed Jul 3 16:19:33 UTC 2013

On Tue, Jul 2, 2013 at 11:38 PM, Robert Collins
<robertc at robertcollins.net> wrote:
> Radix points out I missed the naunce that you're targeting the users
> of python-novaclient, for instance, rather than python-novaclient's
> own tests.
> On 3 July 2013 16:29, Robert Collins <robertc at robertcollins.net> wrote:
>>> What I'd like is for each client library, in addition to the actual
>>> implementation, is that they ship a fake, in-memory, version of the API. The
>>> fake implementations should take the same arguments, have the same return
>>> values, raise the same exceptions, and otherwise be identical, besides the
>>> fact
>>> that they are entirely in memory and never make network requests.
>> So, +1 on shipping a fake reference copy of the API.
>> -1 on shipping it in the client.
>> The server that defines the API should have two implementations - the
>> production one, and a testing fake. The server tests should exercise
>> *both* code paths [e.g. using testscenarios] to ensure there is no
>> skew between them.
>> Then the client tests can be fast and efficient but not subject to
>> implementation skew between fake and prod implementations.
>> Back on Launchpad I designed a similar thing, but with language
>> neutrality as a goal :
>> https://dev.launchpad.net/ArchitectureGuide/ServicesRequirements#Test_fake
>> And in fact, I think that that design would work well here, because we
>> have multiple language bindings - Python, Ruby, PHP, Java, Go etc, and
>> all of them will benefit from a low(ms or less)-latency test fake.
> So taking the aspect I missed into account I'm much happier with the
> idea of shipping a fake in the client, but... AFAICT many of our
> client behaviours are only well defined in the presence of a server
> anyhow.
> So it seems to me that a fast server fake can be used in tests of
> python-novaclient, *and* in tests of code using python-novaclient
> (including for instance, heat itself), and we get to write it just
> once per server, rather than once per server per language binding.
> -Rob

I want to make sure I understond you. Let's say I have a program named
cool-cloud-tool, and it uses python-novaclient, python-keystoneclient,
and three other clients for OpenStack services. You're suggesting that
its test suite should start up instances of all those OpenStack
services with in-memory or otherwise localized backends, and
communicate with them using standard python-*client functionality?

I can imagine that being a useful thing, if it's very easy to do, and
won't increase my test execution time too much.

IRC: radix
Christopher Armstrong

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