A test target having N invisible test data encodements (66.sub.0 -66.sub.N, 74.sub.0 -74.sub.N, 74'.sub.0 -74'.sub.N) each comprising test data printed over the surface of test print media media in a defined spatial order printed in invisible ink by a printer under test. The invisible ink print quality of the printer is determined by the ability of an invisible encodement reader to decode certain of the N invisible encodements (66.sub.0 -66.sub.N, 74.sub.0 -74.sub.N, 74'.sub.0 -74'.sub.N). In a first preferred embodiment, a test print media is prepared by pre-printing or coating a media surface with an invisible ink that is sensitive to the same wavelength of light as the printer ink in a plurality N of areas on the media surface providing step background densities (58.sub.0 -58.sub.N) ranging from no applied ink to maximum printer ink density in a test tablet manner In the test mode, N test data files are printed as N invisible encodements (66.sub.0 -66.sub.N) in the corresponding N areas (58.sub.0 -58.sub.N) thereby creating a test target that is to be read by the reader. It is presumed that the print quality that the printer is capable of achieving is degraded if fewer than a predetermined number of encodements (66.sub.0 -66.sub.N) are readable, and the invisible ink is replaced or replenished. In a second preferred embodiment, the test target comprises N invisible encodements (74.sub.0 -74.sub.N, 74'.sub.0 -74'.sub.N) differing from one another in a step tablet manner printed by the printer (16) under test. The encodements (74.sub.0 -74.sub.N, 74'.sub.0 -74'.sub.N) are read and decoded to the extent possible using the reader. The particular ones of the encodements (74.sub.0 -74.sub.N, 74'.sub.0 -74'.sub.N) that can be accurately decoded provide a measure of the print quality that the printer is capable of achieving.