in-process component(individual micro-service) testing in microservice architecture

I am exploring individual microservice testing & came across a good guide http://ift.tt/2zQ9dWy. This post suggest there is a way to test the individual microservices "in-process".

Which means the test & service will execute in same process, it also provides the lib which can be used. However I am not able to understand following things 1) How exactly "in-process" testing will work in microservice architecture 2) Any pointers on how to use "inproctester" lib.

Thanks