The higher up you go in your component hierarchy, the more likely it is that you'll need a mock component to test them, but I've found that it's possible to str

The higher up you go in your component hierarchy, the more likely it is that you'll need a mock component to test them, but I've found that it's possible to structure your architecture such that you don't need to do it as often as you'd think. If a component is using another component simply to fetch some data it needs (VERY common in my experience), then you could restructure things such that you just pass that data into the component from outside in the first place, possibly even treating it as a simple transformer instead of an actor. There's a limit to this, of course, but keeping this principle in mind in your design also has the effect of bringing coupling to a minimum or even zero in some cases, and promoting re-use of these now completely independent components. When components don't care where or how they get their data, they become a lot simpler due to the elimination of state (implicit and explicit). Elimination of state also facilitates making functions idempotent, which massively reduces cognitive load when reasoning about a system.