Usually, you can test them using a PSP with a fairly recent firmware version by doing this:

1. Start up the PSP with no UMD inserted, and the Memory Stick you want to test inserted in the slot.
2. Go down in the menu until the white logo for the Memory Stick is highlighted, then press the triangle button on the PSP.
3. Select Information.
4. If the Memory Stick is genuine, it will say 'MagicGate Supported' on the third line; if it's fake, it will either say 'MagicGate Not Supported' or 'MagicGate Unknown'.

I hope this helped!

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