World-building environment

In writing my first test using this module, I find myself spending a lot of time writing the code that sets up the environment appropriately (e.g., "ensure enough of the world is loaded, then put dirt here, here, and here"). It's not especially complicated for my particular use-case (yet), but I'm guessing that this sort of thing is a common enough need across enough different modules that I think it may be worth building an extension of ModuleTestingEnvironment that handles some of this for you.

I've been using this code as an example; @kaen has set up a DSL for concisely encoding the world template for the test. The extension I'm envisioning would be similar.

Start by reading ModuleTestingEnvironment and the example FlexibleMovementTestingEnvironment.java linked in the issue. Compare how the example encodes a world template and define the scope of a reusable extension. Done means a proposed environment extension can express common world setup concisely across modules.