Extended Test Coverage

As this project matures and we're publishing regular releases to the public App and Play Stores, we need to begin working toward as much test coverage as possible, and we will integrate it into our existing CI/CD (which is pretty much CD only at the moment) pipeline

Requirements:

* [ ] Jest: Snapshot tests for UI Screens (at least 2)
* [ ] Jest: Coverage for Redux Sages, Actions, and Reducers (coverage for 3-5 most frequently used paths)

See also:

#161

References:

* https://reactjs.org/docs/testing.html
* https://jestjs.io/docs/en/tutorial-react-native
* https://callstack.com/blog/testing-react-native-with-the-new-jest-part-1-snapshots-come-into-play/
* https://callstack.com/blog/testing-react-native-with-the-new-jest-part-2-redux-snapshots-for-your-actions-and-reducers/
* https://redux-saga.js.org/docs/advanced/Testing.html
* https://testing-library.com/docs/react-testing-library/example-intro