Re: [Qemu-devel] [PATCH v3 4/5] qemu-iotests: make python tests attempt to leave intermediate files

[Stefan Hajnoczi <stefanha@redhat.com>]

On Thu, Aug 31, 2017 at 11:47:59AM -0400, Jeff Cody wrote:
> On Thu, Aug 31, 2017 at 04:39:49PM +0100, Stefan Hajnoczi wrote:
> > On Wed, Aug 30, 2017 at 06:40:29PM -0400, John Snow wrote:
> > > 
> > > 
> > > On 08/30/2017 06:35 PM, Eric Blake wrote:
> > > > On 08/30/2017 05:28 PM, John Snow wrote:
> > > > 
> > > >> I'm a little iffy on this patch; I know that ./check can take care of
> > > >> our temp files for us now, but because each python test is itself a
> > > >> little mini-harness, I'm a little leery of moving the teardown to setup
> > > >> and trying to pre-clean the confetti before the test begins.
> > > >>
> > > >> What's the benefit? We still have to clean up these files per-test, but
> > > >> now it's slightly more error-prone and in a weird place.
> > > >>
> > > >> If we want to try to preserve the most-recent-failure-files, perhaps we
> > > >> can define a setting in the python test-runner that allows us to
> > > >> globally skip file cleanup.
> > > > 
> > > > On the other hand, since each test is a mini-harness, globally skipping
> > > > cleanup will make a two-part test fail on the second because of garbage
> > > > left behind by the first.
> > > > 
> > > 
> > > subtext was to have per-subtest files.
> > > 
> > > > Patch 5 adds a comment with another possible solution: teach the python
> > > > mini-harness to either clean all files in the directory, or to relocate
> > > > the directory according to test name, so that each mini-test starts with
> > > > a fresh location, and cleanup is then handled by the harness rather than
> > > > spaghetti pre-cleanup.  But any solution is better than our current
> > > > situation of nothing, so that's why I'm still okay with this patch as-is
> > > > as offering more (even if not perfect) than before.
> > > > 
> > > 
> > > I guess where I am unsure is really if this is better than what we
> > > currently do, which is to (try) to clean up after each test as best as
> > > we can. I don't see it as too different from trying to clean up before
> > > each test.
> > > 
> > > It does give us the ability to leave behind a little detritus after a
> > > failed run, but it's so imperfect that I wonder if it's worth shifting
> > > this code around to change not much.
> > 
> > An alternative is to define iotests.QMPTestCase.setUp() so it clears out
> > iotests.test_dir.  Unfortunately this still requires touching up all
> > setUp() methods so that they call super(TheClass, self).setUp().
> > 
> > At least there would be no need to delete specific files by name (e.g.
> > blind_remove(my_img)).
> > 
> 
> One reason to only remove specific files used in the test, is that it
> increases the chance that intermediate files will be left behind in case of
> test failure of a different test case.
> 
> I think the real long-term solution is to run each unittest test case in its
> own subdirectory, so that no intermediate file removal is necessary, and
> each test case is self-contained.

That could be achieved in the same way:

Modify iotests.QMPTestCase.setUp() to create a new directory and chdir()
into it.  This still requires touching up all existing setUp() methods
to call their superclass.

Stefan