Implement test worker/test framework

[fabiocav]

Implement a test worker and test helpers for public consumption.

This should also be adopted by the worker tests in the project.

[fabiocav]

Work here is in progress, but likely to span across multiple sprints. We'll decompose this issue and assign more granular tasks.

[SeanFeldman]

@fabiocav, I'm assuming once some of that work can be shared, it will be. Looking forward to trying out what's being built.

[joshmouch]

Is there any update on when this would be available?

[davidstarkcab]

Any updates? :)

[newbazz]

do we have any framework to unit test out-of-process azure functions?