Test 1
testimg.ppm:	PPM raw, 227 by 149  maxval 255
testgrid.pbm:	PBM raw, 14 by 16
stdin:	PGM raw, 227 by 149  maxval 255
stdin:	PAM, 227 by 149 by 1 maxval 255
    Tuple type: GRAYSCALE
Test 2
stdin:	3 images
stdin:	Image 0:	PBM raw, 14 by 16
stdin:	Image 1:	PBM raw, 14 by 16
stdin:	Image 2:	PBM raw, 14 by 16
Test 3
227 149
testimg.ppm: PPM RAW 227 149 3 255 RGB
stdin: PBM RAW 14 16 1 1 BLACKANDWHITE
Test Invalid
Expected failure 1 (no output)
Expected failure 2 (no output)
Expected failure 3 (no output)