I test mine by using actual seed.  I open the back cab window and with the engine off, I drop a few seeds down Row 1.  The system should come to life and then start to squeal a second or two after you stop dropping kernels.

The squealing should continue for a while and then stop.  I then repeat the process for each row.  This procedure allows me to do the testing alone although a helper might be useful.

One year this testing caused me some grief.  Rather than mount the display in its bracket I just laid it on the seat and did my testing.  When I crawled back in, I knocked the display to the floor and even though the floor mat was soft and the distance was not great, the display window broke.  After a costly repair by Ag Express I was back in business.