enhance developer UI Testing tab to remember which ruleset was opened

It is annoying for a developer to go to the Testing tab, select an ECI (which is remembered (very nice!)) and then open up the ruleset, but need to check out something in another tab. When you come back to the Testing tab, the rulesets are all closed again.

Could we memoize which rulesets are open in the Testing tab, so that when it renders they are still open?