Q: Hardware test on my macbook pro won't start

You need to be near your or on a Ethernet cable to the router and hold the D key down for like a long time until it appears.

It will go away if you release it, hold the D down before you boot up as it's a hardware firmware command and it's the very first thing the computer loads up once it receives power.

It's working here on my Early 2011, so all I can suggest is your doing it wrong, or there is another problem, perhaps a firmware password?

Reboot holding Command V and if you get a black screen with white type while booting, there is no firmware password.

Try holding down the option key and the D key at the same time

when you hit the power button and that should work.

I had the same problem and that did it.