proj 2 task 3's test case
Merge branch 'master' of https://github.com/bcip/nachos
Merge branch 'master' of https://github.com/bcip/nachos
Merge branch 'master' of https://github.com/bcip/nachos
Merge branch 'master' of https://github.com/bcip/nachos
Merge branch 'master' of https://github.com/bcip/nachos