Adding tests

[iyxan23]

Having tests would ensure zipalign-java works as expected. Lately many bugs have been occurring due to reckless merges by myself.

One question though: what kinds of tests should we do? zipaligning zips and shasum-ing them? if we were to, wouldn't introducing zips to the repo would make it heavier? i don't think people should get test zip files (that may be large) when they're cloning zipalign-java.