Implement test code

Download "shunit2" version 2.1.3 from
http://shunit2.googlecode.com/svn/trunk/source/2.1/doc/shunit2.html
and run "make build" to generate "build/shunit2".
Copy "shunit2" to this project's "test" directory.

ref.
  https://github.com/kaosf/semi-automatic-text-editor
Use Bash instead of Ruby