Since the entire application is split into many relatively small modules, it is easier to understand what each microservice does. The natural consequence of this understanding is that it is also easier to test individual microservices. Testing is also aided by the fact that each microservice typically has a limited scope. After all, it's easier to test just the calendar application than to test the entire Personal Information Management (PIM) suite.
This modularity, however, comes at some cost. Your teams may have a much better understanding of individual microservices, but at the same time they may find it harder to grasp how the entire application is composed. While it shouldn't be necessary to learn all the internal details of the microservices that form an application, the sheer number of relationships between components presents a cognitive challenge. It's good practice to use microservices contracts when using this architectural approach.
