Add missing const in testhelper.h
Add missing const in testhelper.h

Signed-off-by: ChangZhuo Chen (陳昌倬) <3e17fff0ff5a2bf6a82b2512b82f435b16fabafb@gmail.com>

PeterDaveHello/libchewing,mangokingTW/libchewing,mangokingTW/libchewing,robert501128/libchewing,ShengYenPeng/libchewing,czchen/libchewing,bbyykk/libtaigi,robert501128/libchewing,hiunnhue/libchewing,bbyykk/libtaigi,Chocobo1/libchewing,robert501128/libchewing,yan12125/libchewing,simonfork/libchewing,PeterDaveHello/libchewing,kito-cheng/libchewing,hiunnhue/libchewing,chewing/libchewing,cwlin/libchewing,PingNote/libchewing,simonfork/libchewing,ShengYenPeng/libchewing,PingNote/libchewing,chewing/libchewing,kito-cheng/libchewing,ShengYenPeng/libchewing,kito-cheng/libchewing,robert501128/libchewing,PingNote/libchewing,cwlin/libchewing,dimotsai/libchewing,dimotsai/libchewing,PingNote/libchewing,PeterDaveHello/libchewing,cwlin/libchewing,cwlin/libchewing,czchen/libchewing,Chocobo1/libchewing,chewing/libchewing,yan12125/libchewing,simonfork/libchewing,czchen/libchewing,dimotsai/libchewing,dimotsai/libchewing,PeterDaveHello/libchewing,bbyykk/libtaigi,bbyykk/libtaigi,bbyykk/libtaigi,Chocobo1/libchewing,hiunnhue/libchewing,kito-cheng/libchewing,chewing/libchewing,cwlin/libchewing,Chocobo1/libchewing,mangokingTW/libchewing,hiunnhue/libchewing,hiunnhue/libchewing,yan12125/libchewing,yan12125/libchewing,ShengYenPeng/libchewing,Chocobo1/libchewing,mangokingTW/libchewing,simonfork/libchewing,czchen/libchewing