Re: [PATCH v1] lib/hashtable_test.c: add test for the hashtable structure

From: Daniel Latypov <dlatypov@google.com>
To: Rae Moar <rmoar@google.com>
Cc: brendanhiggins@google.com, davidgow@google.com,
	skhan@linuxfoundation.org, kunit-dev@googlegroups.com,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v1] lib/hashtable_test.c: add test for the hashtable structure
Date: Fri, 13 Jan 2023 14:45:29 -0800	[thread overview]
Message-ID: <CAGS_qxqz31x_ya1BhoL=3xXLWnuwcJErdUweGK_tKx2KP_tLYQ@mail.gmail.com> (raw)
In-Reply-To: <CA+GJov4cyXhLnVtSMB8vBzscN0_y4fmSegEJjCr1aY51aCs5Bg@mail.gmail.com>

On Fri, Jan 13, 2023 at 2:23 PM Rae Moar <rmoar@google.com> wrote:

<snip>

> > Note: given x is supposed to point to a or b, I don't know if checking
> > against a.data does us much good.
> > If we're trying to check that hash_add() doesn't mutate the keys and
> > data, this code won't catch it.
> > We'd have to instead do something like
> >   if(x->key != 1 && x->key != 2) KUNIT_FAIL(test, ...);
> >
>
> This seems like a good change to me in combination with changing it to
> x->visited++;.
> Although David's suggestion might be slightly more exhaustive.
> Why wouldn't it be important to check that the key matches the data?

Checks like
  KUNIT_EXPECT_EQ(test, x->data, a.data);
won't do anything, given that x == &a.
We're just comparing x->data to itself.

So we would have to write something instead like
  hash_for_each(hash, bkt, x, node) {
          x->visited++;
          if (x->key == a.key) {
                  KUNIT_EXPECT_EQ(test, x->data, 13);
          } else if (x->key == b.key) {
                  KUNIT_EXPECT_EQ(test, x->data, 10);
          } else { /* some call to KUNIT_FAIL about a bad key */ }
  }

Maybe that's worth it in one of the test cases, but I don't know if
it's necessary to replicate this in the other places where we're
incrementing `visited` by checking keys.

Daniel