A method and apparatus permits use of a tester memory (31) as storage for an inversion mask. The inversion mask indicates to the tester which cells in a DUT memory (14) are logically inverted during testing. Data information and the inverse of the data information is input into a first data multiplexer (802). The stored inversion mask (902-908) is used to independently select a data information bit or its inverse for presentation as a masked output (814) at the output of the first data multiplexer (802).