Re: [PATCH v2 5/6] lib: math_kunit: Add tests for new macros related to rounding to nearest value

[Dave Martin]

On Mon, Aug 26, 2024 at 08:38:21PM +0530, Devarsh Thakkar wrote:
> Add tests for round_closest_up/down and roundclosest macros which round
> to nearest multiple of specified argument. These are tested with kunit
> tool as shared here [1] :

The tests here don't seem to be well targeted at the actual edge cases
where incrementing or decremting the dividend by 1 is expected to
change the result, or when round_closest_up() and round_closest_down()
are expected to differ.

There's also no coverage of:

	* negative inputs

	* types other than int

	* inputs close to type limits

(I've highlighted a few specific issues below, though there seems to be
a more general lack of coverage here.)

> 
> Link: https://gist.github.com/devarsht/3f9042825be3da4e133b8f4eda067876 [1]
> Signed-off-by: Devarsh Thakkar <devarsht@xxxxxx>
> Acked-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> ---
> V2: No change
> ---
>  lib/math/math_kunit.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/lib/math/math_kunit.c b/lib/math/math_kunit.c
> index be27f2afb8e4..05022f010be6 100644
> --- a/lib/math/math_kunit.c
> +++ b/lib/math/math_kunit.c
> @@ -70,6 +70,26 @@ static void round_down_test(struct kunit *test)
>  	KUNIT_EXPECT_EQ(test, round_down((1 << 30) - 1, 1 << 29), 1 << 29);
>  }
>  
> +static void round_closest_up_test(struct kunit *test)
> +{
> +	KUNIT_EXPECT_EQ(test, round_closest_up(17, 4), 16);
> +	KUNIT_EXPECT_EQ(test, round_closest_up(15, 4), 16);
> +	KUNIT_EXPECT_EQ(test, round_closest_up(14, 4), 16);
> +	KUNIT_EXPECT_EQ(test, round_closest_up((1 << 30) - 1, 1 << 30), 1 << 30);
> +	KUNIT_EXPECT_EQ(test, round_closest_up((1 << 30) + 1, 1 << 30), 1 << 30);

These miss the edge case where the result is expected to change; could
we also check:

	round_closest_up(1 << 29, 1 << 30)


> +	KUNIT_EXPECT_EQ(test, round_closest_up((1 << 30) - 1, 2), 1 << 30);
> +}
> +
> +static void round_closest_down_test(struct kunit *test)
> +{
> +	KUNIT_EXPECT_EQ(test, round_closest_down(17, 4), 16);
> +	KUNIT_EXPECT_EQ(test, round_closest_down(15, 4), 16);
> +	KUNIT_EXPECT_EQ(test, round_closest_down(14, 4), 12);
> +	KUNIT_EXPECT_EQ(test, round_closest_down((1 << 30) - 1, 1 << 30), 1 << 30);
> +	KUNIT_EXPECT_EQ(test, round_closest_down((1 << 30) + 1, 1 << 30), 1 << 30);
> +	KUNIT_EXPECT_EQ(test, round_closest_down((1 << 30) - 1, 2), (1 << 30) - 2);
> +}
> +
>  /* These versions can round to numbers that aren't a power of two */
>  static void roundup_test(struct kunit *test)
>  {
> @@ -95,6 +115,18 @@ static void rounddown_test(struct kunit *test)
>  	KUNIT_EXPECT_EQ(test, rounddown(4, 3), 3);
>  }
>  
> +static void roundclosest_test(struct kunit *test)
> +{
> +	KUNIT_EXPECT_EQ(test, roundclosest(21, 5), 20);
> +	KUNIT_EXPECT_EQ(test, roundclosest(19, 5), 20);

This seems to miss the edge cases (e.g., roundclosest(20 * N + 10, 20),
roundclosest(20 * N +/- 9, 20) for some N.

> +	KUNIT_EXPECT_EQ(test, roundclosest(17, 5), 15);
> +	KUNIT_EXPECT_EQ(test, roundclosest((1 << 30), 3), (1 << 30) - 1);
> +	KUNIT_EXPECT_EQ(test, roundclosest((1 << 30) - 1, 1 << 29), 1 << 30);
> +
> +	KUNIT_EXPECT_EQ(test, roundclosest(4, 3), 3);
> +	KUNIT_EXPECT_EQ(test, roundclosest(5, 3), 6);
> +}
> +

[...]

Cheers
---Dave