How to test whether RAM has bad block?

[ac66ub1]

I am using AC66U-B1.If RAM(I mean something like JFFS,NVRAM) has bad block, will cause lots of problem.
I am not sure if there's a method to test it,like HDtune.

 

[RMerlin]

The NAND controller and its driver are designed to handle these automatically. The controller manages a list of known bad blocks to map these.

That's NAND flash btw, not RAM.