Mocha bdd tests

I went through and added Mocha/phantomjs/expectjs/sinonjs for test purposes. I tried to follow current Leaflet testing tools. Having just started to use the esri-leaflet plugin, I added tests as I thought would be applicable. The L.esri.Mixins methods do not have tests yet.
I have a failing test for L.esri.Util.extentToBounds that is flagged to skip, but it could be I am testing this method incorrectly.
I also updated the package.json and added the tasks to run "grunt test".
I usually find test suites to be a great learning tool.

Thanks.