IIRC, that's one of the two methods they use. The "qualitative" gives a binary result, but there are also "quantitative" methods that measure the the actual filtration efficiency with the fit.
That qualitative test kit is probably the cheapest, but it still costs still hundreds of dollars. Though I imagine that's mainly due to low-volume production, since it doesn't seem that complicated.
There are some options for doing fit tests with cheaper equipment. Here's one that uses a humidifier and essential oil diffuser and compares them with the official testing equipment:
That qualitative test kit is probably the cheapest, but it still costs still hundreds of dollars. Though I imagine that's mainly due to low-volume production, since it doesn't seem that complicated.