lib: Move KUnit tests into tests/ subdirectory

Following from the recent KUnit file naming discussion[1], move all
KUnit tests in lib/ into lib/tests/.

Link: https://lore.kernel.org/lkml/20240720165441.it.320-kees@kernel.org/ [1]
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: David Gow <davidgow@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Rae Moar <rmoar@google.com>
Link: https://lore.kernel.org/r/20241202075545.3648096-4-davidgow@google.com
Signed-off-by: Kees Cook <kees@kernel.org>

lib/tests/test_sort.c

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <kunit/test.h>
+
+#include <linux/sort.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+/* a simple boot-time regression test */
+
+#define TEST_LEN 1000
+
+static int cmpint(const void *a, const void *b)
+{
+	return *(int *)a - *(int *)b;
+}
+
+static void test_sort(struct kunit *test)
+{
+	int *a, i, r = 1;
+
+	a = kunit_kmalloc_array(test, TEST_LEN, sizeof(*a), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, a);
+
+	for (i = 0; i < TEST_LEN; i++) {
+		r = (r * 725861) % 6599;
+		a[i] = r;
+	}
+
+	sort(a, TEST_LEN, sizeof(*a), cmpint, NULL);
+
+	for (i = 0; i < TEST_LEN - 1; i++)
+		KUNIT_ASSERT_LE(test, a[i], a[i + 1]);
+
+	r = 48;
+
+	for (i = 0; i < TEST_LEN - 1; i++) {
+		r = (r * 725861) % 6599;
+		a[i] = r;
+	}
+
+	sort(a, TEST_LEN - 1, sizeof(*a), cmpint, NULL);
+
+	for (i = 0; i < TEST_LEN - 2; i++)
+		KUNIT_ASSERT_LE(test, a[i], a[i + 1]);
+}
+
+static struct kunit_case sort_test_cases[] = {
+	KUNIT_CASE(test_sort),
+	{}
+};
+
+static struct kunit_suite sort_test_suite = {
+	.name = "lib_sort",
+	.test_cases = sort_test_cases,
+};
+
+kunit_test_suites(&sort_test_suite);
+
+MODULE_DESCRIPTION("sort() KUnit test suite");
+MODULE_LICENSE("GPL");