Improved testing of the library

Implemented slightly more rigorous tests. The old tests only ran the scripts, but these ones also make sure that the files are generated and uses a temporary directory. 

Run tests by using the `behave` command from the command line in the top level directory of the repository. 
You might need to use:
`pip install behave`
 in order to run it.

The tests were implemented using the [`behave`](http://pythonhosted.org/behave/) library. It encourages a behavior-driven development ([BDD](http://pythonhosted.org/behave/philosophy.html)) by writing tests in [Gherkin](https://github.com/cucumber/cucumber/wiki/Gherkin). One specifies the expected behavior of the program before writing to test the behavior.