Input: tests - add test to cover all input_grab_device() function

Currently input_grab_device() isn't covered by any tests
Thus, adding a test to cover the cases:
1. The device is grabbed successfully
2. Trying to grab a device that is already grabbed by another input
   handle

Signed-off-by: Dana Elfassy <dangel101@gmail.com>
Tested-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/20230522215514.722564-1-dangel101@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: dangel101

drivers/input/tests/input_test.c

@@ -130,10 +130,42 @@ static void input_test_match_device_id(struct kunit *test)
 	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
 }
 
+static void input_test_grab(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+	struct input_handle test_handle;
+	struct input_handler handler;
+	struct input_handle handle;
+	struct input_device_id id;
+	int res;
+
+	handler.name = "handler";
+	handler.id_table = &id;
+
+	handle.dev = input_get_device(input_dev);
+	handle.name = dev_name(&input_dev->dev);
+	handle.handler = &handler;
+	res = input_grab_device(&handle);
+	KUNIT_ASSERT_TRUE(test, res == 0);
+
+	test_handle.dev = input_get_device(input_dev);
+	test_handle.name = dev_name(&input_dev->dev);
+	test_handle.handler = &handler;
+	res = input_grab_device(&test_handle);
+	KUNIT_ASSERT_EQ(test, res, -EBUSY);
+
+	input_release_device(&handle);
+	input_put_device(input_dev);
+	res = input_grab_device(&test_handle);
+	KUNIT_ASSERT_TRUE(test, res == 0);
+	input_put_device(input_dev);
+}
+
 static struct kunit_case input_tests[] = {
 	KUNIT_CASE(input_test_polling),
 	KUNIT_CASE(input_test_timestamp),
 	KUNIT_CASE(input_test_match_device_id),
+	KUNIT_CASE(input_test_grab),
 	{ /* sentinel */ }
 };