I'm trying to recall a phrase commonly used for an effective test that can be done on the fly to diagnose or to assess the quality of something.

It's not a litmus test.

The context, from a lost source, was Schamroth's window test for finger clubbing.

Pass muster is the only phrase that's coming to me right now.

Go/no go?

Undoubtedly the expression you're looking for is "harold larwood"

No, just kidding. That's the first listing for "quick test" in OneLook's reverse dictionary. This approach, however, did turn up "spot check," the only response that seemed remotely applicable among hundreds or thousands that weren't

Nonetheless if all else fails and you're a patient and determined fella, you might go there, entering, for instance, "fast test," "quick check," "running trial," etc etc. Incidentally "quick inspection" turns up "once-over" and "look-over"

http://thesaurus.reference.com/browse/test

"Sanity check" is one I use and have heard used a lot. It's usually a quick check to make sure that your partial results are "in the right ballpark."

Just happened to think - "spot check" is another one that's used with some frequency.

That, however, implies you are only checking a part of the larger whole; like one sample in a number of manufactured items.