Thanks Leif!
Now, on version 3.19.16, test generator works (FM Processor > Misc. > MPX out 1 > Test Gen: square) there is a square wave on analog audio output card.
But, there is also a square wave on MPX out 2 analog audio output.
I think these two analog audio outputs (L and R) should be independent as there are two separate buttons MPX out 1(ch L) and MPX out 2 (ch R) with two separate setups.
This is very important because we have two transmitters connect as following: L channel MPX output 1 goes to main transmitter and R channel MPX output 2 goes to stand by transmitter so test signals on the air is not a good practice.