AHT doesn't work test block at 12 sec

Hi

It is a few months that I think my MacBook needs test using AHT , but it never worked .
When we press " D " and chose the Internet connection , press " Test" .... the first step , 12 seconds ..... nothing more , crashes at this time for 1 hour . I have nothing else to do but to shut down the Mac .

Every test done it (Permission, VRAM, Repair Disk, Software third part to test RAM, clear cache, 2 formats between ML -> Maverick & Mavericks -> Yosemite..)

I have a MacBook Pro 15', mid 2012, i7 2,3Gh.... Nivdia GT650M, 512Mb..... Yosemite 10.10.5

After 2 years I update RAM to 8Gb with certificate apple hardware (buydiffe****.it) last years i try use AHT to test it.. same result.

using another software of testing ram, show no problems all RAM works.

After 3 years I like to test my logic board and Nvidia hardware, many rendering and work have support.... AHT? no works...

Now in January I update also HD to SSD model.

It's a few months that little glitch appear randomly.... NEED AHT!!! Help me!

Davide