You cannot perform your own tests for mycobacteria in water - special incubation is required - you draw the sample from your taps and send it in.

In my opinion, it would be pointless to test your soil - just assume mycobacteria IS there - it comes from animals, air, water... and is ubiquitous. The presence of it is immaterial as long as you protect yourself from inhaling large quantities of it.
Why were you interested in a soil test?
Sue