The compressed texture data, being all 0's, might not be legal to feed to the DXT decompressor. What would happen if the width or height were actually legal? What error would be generated? Can the test distinguish between the two kinds of failures? Is it feasible to generate some actually valid DXT data (perhaps by replicating some known good values over and over again), verify that the test passes if the width and height are in bounds, and then re-run the test with the width and height out of bounds?