[openstack-dev] [all] re-introducing twisted to global-requirements

Robert Collins robertc at robertcollins.net
Wed Jan 13 22:00:16 UTC 2016

On 8 January 2016 at 08:09, Jim Rollenhagen <jim at jimrollenhagen.com> wrote:
> Hi all,
> A change to global-requirements[1] introduces mimic, which is an http
> server that can mock various APIs, including nova and ironic, including
> control of error codes and timeouts. The ironic team plans to use this
> for testing python-ironicclient without standing up a full ironic
> environment.

Whee that was a bit of a thread. Sorry for kicking this off on IRC and
not chiming in until now.

As I read it the following points were made:
  - this is a new an different testing thing
  - which has the same interface skew issues as regular mocks
  - and devs may need to hack twisted to fix issues with it in future
  - but it is being used to target local devs, not gate jobs [today]

Interface skew can be handled a couple of ways. I'm a big fan of a
technique (that I *think* came out of Google) of having a test fake
layer which is substitutable by real things, so you can always run it
in 'slow mode' to make sure things still work with real components.
It's my understanding that with the way mimic is used, this can be
done: run the same tests with real e.g. devstack brought up
components. I think that that is good insurance, particularly if this
is being done periodically rather than

Another way to mitigate interface skew is to have the publisher of an
interface also publish a fast test fake for folk to use. I am also a
fan of doing that, but as we haven't done so yet, I think its ok to go
with what we have. If we couldn't run the same things with a real
implementation, I would be more worried - because mocks of moving
interfaces are fragile (e.g. mocking out oslo.config is fragile vs
mocking out os.unlink).

Personally, I'm fine hacking on Twisted code - I quite like it
(particularly good Twisted code :)) - and since folk seem ok with that
aspect, great - thank you for raising the discussion here.

I look forward to hearing how it goes for Ironic.


Robert Collins <rbtcollins at hpe.com>
Distinguished Technologist
HP Converged Cloud

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