A system and method for testing a data storage device without revealing memory content. To control the individual bits of the memory during testing each value is written into the memory according to the equation NEW_DATA=CURRENT_DATA XOR DATA_SEED such that individual bits of NEW_DATA are equal to CURRENT_DATA with selected bits inverted when the corresponding positions in DATA_SEED are high. NEW_DATA is written into the memory, read out and verified, so that all bit positions can be controlled and tested in both logic states, while NEW_DATA and CURRENT_DATA are not ascertainable by the testing software.