Re: RFC - kernel selftest result documentation (KTAP)

[Brendan Higgins]

On Wed, Jun 10, 2020 at 06:11:06PM +0000, Bird, Tim wrote:
> Some months ago I started work on a document to formalize how
> kselftest implements the TAP specification.  However, I didn't finish
> that work.  Maybe it's time to do so now.
> 
> kselftest has developed a few differences from the original
> TAP specification, and  some extensions that I believe are worth
> documenting.
> 
> Essentially, we have created our own KTAP (kernel TAP)
> format.  I think it is worth documenting our conventions, in order to
> keep everyone on the same page.
> 
> Below is a partially completed document on my understanding
> of KTAP, based on examination of some of the kselftest test
> output.  I have not reconciled this with the kunit output format,
> which I believe has some differences (which maybe we should
> resolve before we get too far into this).
> 
> I submit the document now, before it is finished, because a patch
> was recently introduced to alter one of the result conventions
> (from SKIP='not ok' to SKIP='ok').
> 
> See the document include inline below
> 
> ====== start of ktap-doc-rfc.txt ======

[...]

> --- from here on is not-yet-organized material
> 
> Tip:
>  - don't change the test plan based on skipped tests.
>    - it is better to report that a test case was skipped, than to
>      not report it
>    - that is, don't adjust the number of test cases based on skipped
>      tests
> 
> Other things to mention:
> TAP13 elements not used:
>  - yaml for diagnostic messages

We talked about this before, but I would like some way to get failed
expectation/assertion information in the test in a consistent machine
parsible way. Currently we do the following:

    # Subtest: example
    1..1
    # example_simple_test: initializing
    # example_simple_test: EXPECTATION FAILED at lib/kunit/kunit-example-test.c:29
    Expected 1 + 1 == 3, but
        1 + 1 == 2
        3 == 3
    not ok 1 - example_simple_test
not ok 5 - example

Technically not TAP compliant, but no one seems to mind. I am okay with
keeping it the way it is, but if we don't want it in the KTAP spec, we
will need some kind of recourse.

>    - reason: try to keep things line-based, since output from other things
>    may be interspersed with messages from the test itself
>  - TODO directive

Is this more of stating a fact or desire? We don't use TODO either, but
it looks like it could be useful.

> KTAP Extensions beyond TAP13:
>  - nesting
>    - via indentation
>      - indentation makes it easier for humans to read
>  - test identifier
>     - multiple parts, separated by ':'

Can you elabroate on this more? I am not sure what you mean.

>  - summary lines
>    - can be skipped by CI systems that do their own calculations
> 
> Other notes:
>  - automatic assignment of result status based on exit code
> 
> Tips:
>  - do NOT describe the result in the test line
>    - the test case description should be the same whether the test
>      succeeds or fails
>    - use diagnostic lines to describe or explain results, if this is
>      desirable
>  - test numbers are considered harmful
>    - test harnesses should use the test description as the identifier
>    - test numbers change when testcases are added or removed
>      - which means that results can't be compared between different
>        versions of the test
>  - recommendations for diagnostic messages:
>    - reason for failure
>    - reason for skip
>    - diagnostic data should always preceding the result line
>      - problem: harness may emit result before test can do assessment
>        to determine reason for result
>      - this is what the kernel uses
> 
> Differences between kernel test result format and TAP13:
>  - in KTAP the "# SKIP" directive is placed after the description on
>    the test result line
> 
> ====== start of ktap-doc-rfc.txt ======
> OK - that's the end of the RFC doc.
> 
> Here are a few questions:
>  - is this document desired or not?
>     - is it too long or too short?
>  - if the document is desired, where should it be placed?

I like it. I don't think we can rely on the TAP people updating their
stuff based on my interactions with them. So having a spec which is
actually maintained would be nice.

Maybe in Documentation/dev-tools/ ?

>    I assume somewhere under Documentation, and put into
>    .rst format. Suggestions for a name and location are welcome.
>  - is this document accurate?
>    I think KUNIT does a few things differently than this description.
>    - is the intent to have kunit and kselftest have the same output format?
>       if so, then these should be rationalized.

Yeah, I think it would be nice if all test frameworks/libraries for the
kernel output tests in the same language.

Cheers