Within workbench you can test by clicking your trigger condition to preview your change. But for external impact of the rule you have to use "save all".
You can try checking the priority of different rules, rule within other rule groups which may have same trigger conditions. - Try to use built in JSP reference application to preview your changes (supplemental objects #1 should give you a clue to which rule fired).
This is by design you have to use "Save All" and get a confirmation before you can see the changes registered.