test pattern on the substrate 332 that are then analyzed to identify inoperative inkjets in another embodiment shown in fig5 the optical sensor module 300 u2032 is formed with an endless belt substrate for the printing of the test pattern the module 300 u2032 is also configured to fit within area 112 of printer 60 using like numbers for like components the module 300 u2032 includes an optical sensor 304 an endless substrate belt 310 entrained about three rollers 314 one or more actuators 316 a waste receptacle 322 a controller 324 a cleaning member 344 and a tensioning mechanism 348 the optical sensor 304 is mounted for movement along guide rail 328 and the guide rail 328 is operatively connected to an actuator 316 to enable the optical sensor 304 to be moved between two positions one position for the optical sensor 304 over the endless substrate 310 enables the test pattern to be printed and the other position over the endless substrate 310 enables the optical sensor 304 to generate measurements of the test pattern on the endless substrate the controller 324 is operatively connected to the actuators 316 to move the optical sensor 304 and guide rail as described to drive at least one roller 314 to rotate the endless substrate 310 and to engage the endless substrate 310 with the cleaning member 344 the cleaning member 344 removes test pattern material from the endless substrate and lets it fall into the waste receptacle 322 alternatively the guide rail 328 and the optical sensor 304 can be fixedly mounted to the printhead.