Comment by M95D

> take a sample of their saliva, run it through a very expensive machine for a few days and decode the results with a supercomputer

You are probably thinking about PCR [0].

The PCR thermocycler is now a very very cheap machine (~ 200$). You could even build one at home. All the other things you need are also cheap. The reaction takes a couple of hours at most and the results are read with an ordinary chemical stain for DNA, possibly an electrophoresis machine and an ordinary computer flatbed scanner, if you want to get fancy. There's no need for a supercomputer - a 486 could do it (and they did, back then).

But you don't even need PCR. There's a very simple Barr Test [1] that you can perform with a glass slide, a chemical stain and a microscope. Result ready in less than an hour.

[0] https://en.wikipedia.org/wiki/Polymerase_chain_reaction

[1] https://labpedia.net/barr-bodies-detection-and-drumstick/