Improve unit testing page in docs

[ffxsam]

https://vuejs.org/v2/guide/unit-testing.html

This page leaves a lot to be desired. How do we simulate events on DOM elements, for example? Is there a more in-depth guide on unit testing in Vue?

[sdras]

We've got a unit testing cookbook article that's almost ready, so this will be done and linked to soon.

[ffxsam]

Thanks Sarah! I actually just discovered vue-test-utils which is the 💣 😄

[sdras]

Totally! I'll be sure to add a link to that too.