Added initial testing framework

Hi!

I think this module is totally underrated. I would like to help add to it.

But before I do, I would like to add tests to make sure I don't break anything. 

If this is accepted, I'll add more tests.

Also, FYI, my simple first test actually did fail because on very recent versions of concat, you can't call concat::setup directly: https://github.com/puppetlabs/puppetlabs-concat/blob/master/manifests/setup.pp

So.. hooray tests? I've locked the concat module version for now to get them to pass.