You can test a 4-20mA sensor with a $10 multimeter and a portable power supply.

Many times we swap out sensors while troubleshooting and need to test them later without connecting them to the control system. Most 4-20mA sensors are powered by 10 to 24 VDC so we can take the PLC Tools SIM-ALP2 in voltage mode and power them up. For this sensor, pin 1 is +power, pin 2 is the analog signal, and pin 3 is -power.