list: test: Add a test for list_entry_is_head()

The list_entry_is_head() macro was added[1] after the list KUnit tests,
so wasn't tested. Add a new KUnit test to complete the set.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e130816164e244b692921de49771eeb28205152dSigned-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

@@ -549,6 +549,26 @@ static void list_test_list_entry(struct kunit *test)
 				struct list_test_struct, list));
 }
 
+static void list_test_list_entry_is_head(struct kunit *test)
+{
+	struct list_test_struct test_struct1, test_struct2, test_struct3;
+
+	INIT_LIST_HEAD(&test_struct1.list);
+	INIT_LIST_HEAD(&test_struct3.list);
+
+	list_add_tail(&test_struct2.list, &test_struct1.list);
+
+	KUNIT_EXPECT_TRUE_MSG(test,
+		list_entry_is_head((&test_struct1), &test_struct1.list, list),
+		"Head element of same list");
+	KUNIT_EXPECT_FALSE_MSG(test,
+		list_entry_is_head((&test_struct2), &test_struct1.list, list),
+		"Non-head element of same list");
+	KUNIT_EXPECT_FALSE_MSG(test,
+		list_entry_is_head((&test_struct3), &test_struct1.list, list),
+		"Head element of different list");
+}
+
 static void list_test_list_first_entry(struct kunit *test)
 {
 	struct list_test_struct test_struct1, test_struct2;
@@ -764,6 +784,7 @@ static struct kunit_case list_test_cases[] = {
 	KUNIT_CASE(list_test_list_splice_init),
 	KUNIT_CASE(list_test_list_splice_tail_init),
 	KUNIT_CASE(list_test_list_entry),
+	KUNIT_CASE(list_test_list_entry_is_head),
 	KUNIT_CASE(list_test_list_first_entry),
 	KUNIT_CASE(list_test_list_last_entry),
 	KUNIT_CASE(list_test_list_first_entry_or_null),