Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210129022555.2411999-1-dlatypov@google.com>
In-Reply-To: <20210129022555.2411999-1-dlatypov@google.com>
From:   Brendan Higgins <brendanhiggins@google.com>
Date:   Fri, 29 Jan 2021 12:07:56 -0800
Message-ID: <CAFd5g44DrzNdDZnaHYAHt48c6+gNPpGwULYxaF=ENGWmMUomLg@mail.gmail.com>
Subject: Re: [PATCH] kunit: don't show `1 == 1` in failed assertion messages
To:     Daniel Latypov <dlatypov@google.com>
Cc:     David Gow <davidgow@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Shuah Khan <skhan@linuxfoundation.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Jan 28, 2021 at 6:26 PM Daniel Latypov <dlatypov@google.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@google.com>

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

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