Add tests and an example for 01

Added tests and an example.rb like later examples have. 

Because this is the first example it seemed reasonable to have a spoiler alert on the example.rb (since my students were pouring over the example.rb on the first day we tried the examples until they realized what it was and quickly quit reading it). 

I also wasn't sure what the best way to test the extensions. Maybe best to have multiple different example files and just accepting duplication? That seems easier than subclassing but it seemed prudent to introduce more complicated concepts in the extensions since they have more time for self-study on the weekend.