Setup unit testing with BATS

[tgharold]

https://github.com/sstephenson/bats

Bats: Bash Automated Testing System
Bats is a TAP-compliant testing framework for Bash. It provides a simple way to verify that the UNIX programs you write behave as expected.

A Bats test file is a Bash script with special syntax for defining test cases. Under the hood, each test case is just a function with a description.