Add non-emulator tests and simplify internal API

A lot of the purely internal API is using constructs which are not needed for internal APIs. The internal API can be viewed and changed by any contributor, so its better to not cover all possible future uses. Indeed to keep the codebase simple, it should be the opposite: the app's code should reflect what is actually happening now, not what might happen in the future.

This also adds tests that run on the JVM rather than the emulator.

These commits where originally in !248 (merged) but I'm submitting them separately since !248 (merged) is too big.