RE: [PATCH linux-kselftest/test v2] ext4: add kunit test for decoding extended timestamps

From: <Tim.Bird@sony.com>
To: <brendanhiggins@google.com>
Cc: <tytso@mit.edu>, <skhan@linuxfoundation.org>,
	<yzaikin@google.com>, <linux-kselftest@vger.kernel.org>,
	<linux-ext4@vger.kernel.org>, <adilger.kernel@dilger.ca>,
	<kunit-dev@googlegroups.com>
Subject: RE: [PATCH linux-kselftest/test v2] ext4: add kunit test for decoding extended timestamps
Date: Fri, 18 Oct 2019 01:30:42 +0000	[thread overview]
Message-ID: <ECADFF3FD767C149AD96A924E7EA6EAF977D01A2@USCULXMSG01.am.sony.com> (raw)
In-Reply-To: <CAFd5g44txp2j9May1YD9rq6bcNnCx_JKNNmnsrr+JG+cTX0chg@mail.gmail.com>

> -----Original Message-----
> From: Brendan Higgins 
> 
> On Thu, Oct 17, 2019 at 3:25 PM <Tim.Bird@sony.com> wrote:
> >
> > > -----Original Message-----
> > > From: Theodore Y. Ts'o on October 17, 2019 2:09 AM
> > >
> > > On Wed, Oct 16, 2019 at 05:26:29PM -0600, Shuah Khan wrote:
> > > >
> > > > I don't really buy the argument that unit tests should be deterministic
> > > > Possibly, but I would opt for having the ability to feed test data.
> > >
> > > I strongly believe that unit tests should be deterministic.
> > > Non-deterministic tests are essentially fuzz tests.  And fuzz tests
> > > should be different from unit tests.
> >
> > I'm not sure I have the entire context here, but I think deterministic
> > might not be the right word, or it might not capture the exact meaning
> > intended.
> >
> > I think there are multiple issues here:
> >  1. Does the test enclose all its data, including working data and expected
> results?
> > Or, does the test allow someone to provide working data?  This alternative
> > implies that either the some of testcases or the results might be different
> depending on
> > the data that is provided.  IMHO the test would be deterministic if it always
> produced
> > the same results based on the same data inputs.  And if the input data was
> deterministic.
> > I would call this a data-driven test.
> >
> > Since the results would be dependent on the data provided, the results
> > from tests using different data would not be comparable.  Essentially,
> > changing the input data changes the test so maybe it's best to consider
> > this a different test.  Like 'test-with-data-A' and 'test-with-data-B'.
> 
> That kind of sound like parameterized tests[1]; 

...

> 
> [1] https://dzone.com/articles/junit-parameterized-test

Both Iurii and you pointed me at parameterized tests.  This sounds like
what I am talking about.  We have a lot of infrastructure for these concepts in Fuego,
but it's called something different.

I'm not sure if I should feel smart for having developed some of these concepts
independently or dumb for not having known about this (apparently) standard
nomenclature. ;-)

Thanks for the reference!
 -- Tim