1. A method of testing a data storage device, comprising: reading a current value of a memory location in the data storage device, the current value comprising a plurality of bits of data, writing a new value into the same memory location in the data storage device, the new value comprising the current value wherein at least one of the plurality of bits of data is inverted, writing a copy of the new value into a data-written register, reading the new value out of the data storage device, comparing the new value read out of the data storage device to the corresponding new value in the data-written register to verify the accuracy of the new value read out of the data storage device.