You can’t have MySQL do this for you automatically for InnoDB tables – you would need to use a trigger or procedure, or user another DB engine such as MyISAM. Auto incrementing can only be done for a single primary key.
Something like the following should work
DELIMITER $$
CREATE TRIGGER xxx BEFORE INSERT ON issue_log
FOR EACH ROW BEGIN
SET NEW.sr_no = (
SELECT IFNULL(MAX(sr_no), 0) + 1
FROM issue_log
WHERE app_id = NEW.app_id
AND test_id = NEW.test_id
);
END $$
DELIMITER ;