Add tape tests for testling

Hey there,

I am not very familiar with [testling](https://ci.testling.com/guide/quick_start), but I think there should be unit tests for this module. The tests right now do not cover the full functionality and need to be extended, but are at least a start, so that we can begin using Testling CI for this module. 

I moved the test to `example.js` (can be run with npm start), because I guess that's more what it actually is right now - and it's quite useful since it shows the real behavior in the browser (which I didn't yet cover properly).

The test pass in the current version of Chrome for me.

Best,
Finn