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Date:   Sat, 14 Nov 2020 01:14:15 +0100
From:   Marco Elver <elver@...gle.com>
To:     David Gow <davidgow@...gle.com>
Cc:     "Bird, Tim" <Tim.Bird@...y.com>,
        Arpitha Raghunandan <98.arpi@...il.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-kernel-mentees@...ts.linuxfoundation.org" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v6 1/2] kunit: Support for Parameterized Testing

On Fri, 13 Nov 2020 at 23:37, David Gow <davidgow@...gle.com> wrote:
>
> On Fri, Nov 13, 2020 at 6:31 PM Marco Elver <elver@...gle.com> wrote:
> >
> > On Fri, Nov 13, 2020 at 01:17PM +0800, David Gow wrote:
> > > On Thu, Nov 12, 2020 at 8:37 PM Marco Elver <elver@...gle.com> wrote:
> > [...]
> > > > > (It also might be a little tricky with the current implementation to
> > > > > produce the test plan, as the parameters come from a generator, and I
> > > > > don't think there's a way of getting the number of parameters ahead of
> > > > > time. That's a problem with the sub-subtest model, too, though at
> > > > > least there it's a little more isolated from other tests.)
> > > >
> > > > The whole point of generators, as I envisage it, is to also provide the
> > > > ability for varying parameters dependent on e.g. environment,
> > > > configuration, number of CPUs, etc. The current array-based generator is
> > > > the simplest possible use-case.
> > > >
> > > > However, we *can* require generators generate a deterministic number of
> > > > parameters when called multiple times on the same system.
> > >
> > > I think this is a reasonable compromise, though it's not actually
> > > essential. As I understand the TAP spec, the test plan is actually
> > > optional (and/or can be at the end of the sequence of tests), though
> > > kunit_tool currently only supports having it at the beginning (which
> > > is strongly preferred by the spec anyway). I think we could get away
> > > with having it at the bottom of the subtest results though, which
> > > would save having to run the generator twice, when subtest support is
> > > added to kunit_tool.
> >
> > I can't find this in the TAP spec, where should I look? Perhaps we
> > shouldn't venture too far off the beaten path, given we might not be the
> > only ones that want to parse this output.
> >
>
> It's in the "Test Lines and the Plan" section:
> "The plan is optional but if there is a plan before the test points it
> must be the first non-diagnostic line output by the test file. In
> certain instances a test file may not know how many test points it
> will ultimately be running. In this case the plan can be the last
> non-diagnostic line in the output. The plan cannot appear in the
> middle of the output, nor can it appear more than once."

Ah, that's fine then.

> My only concern with running through the generator multiple times to
> get the count is that it might be slow and/or more difficult if
> someone uses a more complicated generator. I can't think of anything
> specific yet, though, so we can always do it for now and change it
> later if a problematic case occurs.

I'm all for simplicity, so if nobody objects, let's just get rid of
the number of parameters and avoid running it twice.

> > > > To that end, I propose a v7 (below) that takes care of getting number of
> > > > parameters (and also displays descriptions for each parameter where
> > > > available).
> > > >
> > > > Now it is up to you how you want to turn the output from diagnostic
> > > > lines into something TAP compliant, because now we have the number of
> > > > parameters and can turn it into a subsubtest. But I think kunit-tool
> > > > doesn't understand subsubtests yet, so I suggest we take these patches,
> > > > and then somebody can prepare kunit-tool.
> > > >
> > >
> > > This sounds good to me. The only thing I'm not sure about is the
> > > format of the parameter description: thus far test names be valid C
> > > identifier names, due to the fact they're named after the test
> > > function. I don't think there's a fundamental reason parameters (and
> > > hence, potentially, subsubtests) need to follow that convention as
> > > well, but it does look a bit odd.  Equally, the square brackets around
> > > the description shouldn't be necessary according to the TAP spec, but
> > > do seem to make things a little more readable, particuarly with the
> > > names in the ext4 inode test. I'm not too worried about either of
> > > those, though: I'm sure it'll look fine once I've got used to it.
> >
> > The parameter description doesn't need to be a C identifier. At least
> > that's what I could immediately glean from TAP v13 spec (I'm looking
> > here: https://testanything.org/tap-version-13-specification.html and see
> > e.g. "ok 1 - Input file opened" ...).
> >
>
> Yeah: it looked a bit weird for everything else to be an identifier
> (given that KUnit does require it for tests), but these parameter
> descriptions not to be. It's not a problem, though, so let's go ahead
> with it.
>
> > [...]
> > > > > In any case, I'm happy to leave the final decision here to Arpitha and
> > > > > Marco, so long as we don't actually violate the TAP/KTAP spec and
> > > > > kunit_tool is able to read at least the top-level result. My
> > > > > preference is still to go either with the "# [test_case->name]:
> > > > > [ok|not ok] [index] - param-[index]", or to get rid of the
> > > > > per-parameter results entirely for now (or just print out a diagnostic
> > > > > message on failure). In any case, it's a decision we can revisit once
> > > > > we have support for named parameters, better tooling, or a better idea
> > > > > of how people are actually using this.
> > > >
> > > > Right, so I think we'll be in a better place if we implement: 1)
> > > > parameter to description conversion support, 2) counting parameters. So
> > > > I decided to see what it looks like, and it wasn't too bad. I just don't
> > > > know how you want to fix kunit-tool to make these non-diagnostic lines
> > > > and not complain, but as I said, it'd be good to not block these
> > > > patches.
> > >
> > > Yup, I tried this v7, and it looks good to me. The kunit_tool work
> > > will probably be a touch more involved, so I definitely don't want to
> > > hold up supporting this on that.
> > >
> > > My only thoughts on the v7 patch are:
> > > - I don't think we actually need the parameter count yet (or perhaps
> > > ever if we go with subtests as planned), so I be okay with getting rid
> > > of that.
> >
> > As noted above, perhaps we should keep it for compatibility with other
> > parsers and CI systems we don't have much control over. It'd be a shame
> > if 99% of KUnit output can be parsed by some partially compliant parser,
> > yet this would break it.
>
> KUnit has only started providing the test plans in some cases pretty
> recently, and the spec does make it optional, so I'm not particularly
> worried about this breaking parsers. I'm not too worried about it
> causing problems to have it either, though, so if you'd rather keep
> it, that's fine by me as well.
>
> > > - It'd be a possibility to get rid of the square brackets from the
> > > output, and if we still want them, make them part of the test itself:
> > > if this were TAP formatted, those brackets would be part of the
> > > subsubtest name.
> >
> > I don't mind. It's just that we can't prescribe a format, and as
> > seen below the descriptions include characters -<>=,. which can be
> > confusing. But perhaps you're right, so let's remove them.
> >
> > But as noted, TAP doesn't seem to care. So let's remove them.
> >
>
> Yeah: I have a slight preference for removing them, as TAP parsers
> would otherwise include them in the parameter name, which looks a
> little weird.
> Of course, the point is moot until we actually fix kunit_tool and make
> these subtests, so there's no fundamental reason we couldn't leave
> them in for now, and remove them then if you thought it was
> significantly more readable. (Personally, I'd still err on the side of
> removing them to avoid any unnecessary churn.)

Sounds good.

Arpitha: Do you want to send v7, but with the following modifications
from what I proposed? Assuming nobody objects.

1. Remove the num_params counter and don't print the number of params
anymore, nor do validation that generators are deterministic.
2. Remove the [].
[ I'm happy to send as well, just let me know what you prefer. ]

Thanks,
-- Marco

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