lib/math/rational: add Kunit test cases

Adds a number of test cases that cover a range of possible code paths.

[akpm@linux-foundation.org: remove non-ascii characters, fix whitespace]
[colin.king@canonical.com: fix spelling mistake "demominator" -> "denominator"]
  Link: https://lkml.kernel.org/r/20210526085049.6393-1-colin.king@canonical.com

Link: https://lkml.kernel.org/r/20210525144250.214670-2-tpiepho@gmail.com
Signed-off-by: Trent Piepho <tpiepho@gmail.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Daniel Latypov <dlatypov@google.com>
Cc: Oskar Schirmer <oskar@scara.com>
Cc: Yiyuan Guo <yguoaz@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -2444,6 +2444,18 @@ config SLUB_KUNIT_TEST
 
 	  If unsure, say N.
 
+config RATIONAL_KUNIT_TEST
+	tristate "KUnit test for rational.c" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	select RATIONAL
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the rational math unit test.
+	  For more information on KUnit and unit tests in general please refer
+	  to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+	  If unsure, say N.
+
 config TEST_UDELAY
 	tristate "udelay test driver"
 	help

lib/math/Makefile

@@ -6,3 +6,4 @@ obj-$(CONFIG_PRIME_NUMBERS)	+= prime_numbers.o
 obj-$(CONFIG_RATIONAL)		+= rational.o
 
 obj-$(CONFIG_TEST_DIV64)	+= test_div64.o
+obj-$(CONFIG_RATIONAL_KUNIT_TEST) += rational-test.o

lib/math/rational-test.c

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <kunit/test.h>
+
+#include <linux/rational.h>
+
+struct rational_test_param {
+	unsigned long num, den;
+	unsigned long max_num, max_den;
+	unsigned long exp_num, exp_den;
+
+	const char *name;
+};
+
+static const struct rational_test_param test_parameters[] = {
+	{ 1230,	10,	100, 20,	100, 1,    "Exceeds bounds, semi-convergent term > 1/2 last term" },
+	{ 34567,100, 	120, 20,	120, 1,    "Exceeds bounds, semi-convergent term < 1/2 last term" },
+	{ 1, 30,	100, 10,	0, 1,	   "Closest to zero" },
+	{ 1, 19,	100, 10,	1, 10,     "Closest to smallest non-zero" },
+	{ 27,32,	16, 16,		11, 13,    "Use convergent" },
+	{ 1155, 7735,	255, 255,	33, 221,   "Exact answer" },
+	{ 87, 32,	70, 32,		68, 25,    "Semiconvergent, numerator limit" },
+	{ 14533, 4626,	15000, 2400,	7433, 2366, "Semiconvergent, denominator limit" },
+};
+
+static void get_desc(const struct rational_test_param *param, char *desc)
+{
+	strscpy(desc, param->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+/* Creates function rational_gen_params */
+KUNIT_ARRAY_PARAM(rational, test_parameters, get_desc);
+
+static void rational_test(struct kunit *test)
+{
+	const struct rational_test_param *param = (const struct rational_test_param *)test->param_value;
+	unsigned long n = 0, d = 0;
+
+	rational_best_approximation(param->num, param->den, param->max_num, param->max_den, &n, &d);
+	KUNIT_EXPECT_EQ(test, n, param->exp_num);
+	KUNIT_EXPECT_EQ(test, d, param->exp_den);
+}
+
+static struct kunit_case rational_test_cases[] = {
+	KUNIT_CASE_PARAM(rational_test, rational_gen_params),
+	{}
+};
+
+static struct kunit_suite rational_test_suite = {
+	.name = "rational",
+	.test_cases = rational_test_cases,
+};
+
+kunit_test_suites(&rational_test_suite);
+
+MODULE_LICENSE("GPL v2");