list: test: Add a test for list_is_head()

list_is_head() was added recently[1], and didn't have a KUnit test. The
implementation is trivial, so it's not a particularly exciting test, but
it'd be nice to get back to full coverage of the list functions.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/include/linux/list.h?id=0425473037db40d9e322631f2d4dc6ef51f97e88Signed-off-by: David Gow <davidgow@google.com>
Acked-by: Daniel Latypov <dlatypov@google.com>
Acked-by: Brendan Higgins <brendanhiggins@google.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

lib/list-test.c

@@ -254,6 +254,24 @@ static void list_test_list_bulk_move_tail(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, i, 2);
 }
 
+static void list_test_list_is_head(struct kunit *test)
+{
+	struct list_head a, b, c;
+
+	/* Two lists: [a] -> b, [c] */
+	INIT_LIST_HEAD(&a);
+	INIT_LIST_HEAD(&c);
+	list_add_tail(&b, &a);
+
+	KUNIT_EXPECT_TRUE_MSG(test, list_is_head(&a, &a),
+		"Head element of same list");
+	KUNIT_EXPECT_FALSE_MSG(test, list_is_head(&a, &b),
+		"Non-head element of same list");
+	KUNIT_EXPECT_FALSE_MSG(test, list_is_head(&a, &c),
+		"Head element of different list");
+}
+
+
 static void list_test_list_is_first(struct kunit *test)
 {
 	struct list_head a, b;
@@ -731,6 +749,7 @@ static struct kunit_case list_test_cases[] = {
 	KUNIT_CASE(list_test_list_move),
 	KUNIT_CASE(list_test_list_move_tail),
 	KUNIT_CASE(list_test_list_bulk_move_tail),
+	KUNIT_CASE(list_test_list_is_head),
 	KUNIT_CASE(list_test_list_is_first),
 	KUNIT_CASE(list_test_list_is_last),
 	KUNIT_CASE(list_test_list_empty),