I'm seeng test1234 on the aircraft list

Does anyone know why I’m seeing “Test1234” in my aircraft list? At times I see multiple lines of it. No squawk data but message count and seen count.

Where does that come from?

Thanks.

HI Don, I see them in the UK too. No idea what they are.

Nearby maintenance facility testing adsb transmitter gear?

I believe they are ground test stations for triangulation systems used to track non ADS-B airplanes on the airport runways and taxiways. System health can be monitored by comparing the test station’s calculated position with its known position.