How do I get my Ford stang 2012 radiator fan to work
Have you tested the fan to see if it spins when connected to 12 volts?
No. Where do I buy the tester at and what's the cost
There is no "tester". You hotwire the fan to the battery and see if it works.
It would also be a good idea to check fuses and relays.
On that one you may want to check the wiring connector to the fan and fan resistor.
Ford had a problem with them for over a decade.
The resistor can begin to fail and cause the circuit to overheat.
When that occurs this happens to the wiring connectors in the fan circuit.

Sometimes the damage is less and sometimes the damage is worse but there can't be any heat damage at all in these connectors or they have to be replaced along with the resistor.
It's easy to check, only takes a few minutes, and you don't even need any tools to do it.
There's plenty of youtubes out there because like I said, this has been happening for years. So watch a few videos and familiarize yourself with the location of the wiring connectors