A test for what, exactly? A fire puts out a lot of stuff besides particulates. An N95 won't filter any of the gaseous fumes, so in that sense, it's no better than a wet rag. But it should trap a good portion of particulate pollution since most particles will be large enough to be stopped.

In related personal news, that tightness I felt in my chest has gone away once I spent some time indoors again, so no need for wearing a mask to bed tonight. That's good, since it's tough to keep them on when you sleep, let alone keep them from getting crushed and mussed up if you roll over onto them.