linux-kernel - Re: [PATCH] kunit: don't show `1 == 1` in failed assertion messages

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Date:   Fri, 29 Jan 2021 12:07:56 -0800
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Daniel Latypov <dlatypov@...gle.com>
Cc:     David Gow <davidgow@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] kunit: don't show `1 == 1` in failed assertion messages

On Thu, Jan 28, 2021 at 6:26 PM Daniel Latypov <dlatypov@...gle.com> wrote:
>
> Currently, given something (fairly dystopian) like
> > KUNIT_EXPECT_EQ(test, 2 + 2, 5)
>
> KUnit will prints a failure message like this.
> >  Expected 2 + 2 == 5, but
> >      2 + 2 == 4
> >      5 == 5
>
> With this patch, the output just becomes
> >  Expected 2 + 2 == 5, but
> >      2 + 2 == 4
>
> This patch is slightly hacky, but it's quite common* to compare an
> expression to a literal integer value, so this can make KUnit less
> chatty in many cases. (This patch also fixes variants like
> KUNIT_EXPECT_GT, LE, et al.).
>
> It also allocates an additional string briefly, but given this only
> happens on test failures, it doesn't seem too bad a tradeoff.
> Also, in most cases it'll realize the lengths are unequal and bail out
> before the allocation.
>
> We could save the result of the formatted string to avoid wasting this
> extra work, but it felt cleaner to leave it as-is.
>
> Edge case: for something silly and unrealistic like
> > KUNIT_EXPECT_EQ(test, 4, 5);
>
> It'll generate this message with a trailing "but"
> >  Expected 2 + 2 == 5, but
> >  <next line of normal output>
>
> It didn't feel worth adding a check up-front to see if both sides are
> literals to handle this better.
>
> *A quick grep suggests 100+ comparisons to an integer literal as the
> right hand side.
>
> Signed-off-by: Daniel Latypov <dlatypov@...gle.com>

I don't feel very strongly about this either way. In any case:

Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>