Improve user unit testing story in v3

[hossam-nasr]

Related to discussion here, and issues #257 and #160.

With v3, we have an opportunity to be more mindful about how we support users' unit testing story, and include APIs, samples, guides, documentation for unit testing

[hossam-nasr]

Fixing this bug #378 should be an important piece of this work

[davidmrdavid]

@hossam-nasr: Once this is addressed, we should document the unit testing strategy so that it can be a permanent fixture of the experience. I think putting it on mslearn would be best.