tests: add libpostproc test

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

tests/lavfi-regression.sh

@@ -38,6 +38,7 @@ do_lavfi "fade"               "fade=in:5:15,fade=out:30:15"
 do_lavfi "null"               "null"
 do_lavfi "overlay"            "split[m],scale=88:72,pad=96:80:4:4[o2];[m]fifo,[o2]overlay=240:16"
 do_lavfi "pad"                "pad=iw*1.5:ih*1.5:iw*0.3:ih*0.2"
+do_lavfi "pp"                 "mp=pp=de/tn/l5/al"
 do_lavfi "scale200"           "scale=200:200"
 do_lavfi "scale500"           "scale=500:500"
 do_lavfi "select"             "select=not(eq(mod(n\,2)\,0)+eq(mod(n\,3)\,0))"

tests/ref/lavfi/pp

+pp                  3ddfb037bb1f941d6526a2473a191677