Also, this is probably the single biggest difference for me when working with a static vs. dynamically typed language. With Static Typing, there's a "translate the dependency's types into the application's types" step that pretty much screams "put a seam here!". With Dynamic Typing, it's a bit less loud.
I was referring to that, with Scala, I like to avoid leaking the innards of a JSON serialization library in the code for an API client, instead returning domain objects. Whereas with, JS or Python, the initial approach is to sling around the blob of JSON.
