Had trouble debugging D4508 because I couldn't "attach" debugger to hermes in time for message-reducer.js:SET_MESSAGE_STORE_MESSAGES to hit.
Ended up testing via console.log(...) and pasting values into a text file to ensure that things were as expected. The stuff I jotted down lent itself well to writing basic unit tests so figured I might as well put it up.
Depends on D4508