Enhancement: Add Tests

As the app grows, we will really need a test module to test its functionality. It seems like [electron-mocha](https://github.com/jprichardson/electron-mocha) is a popular choice of test framework for electron apps.

Review the app's Electron and Node.js structure and evaluate how electron-mocha could provide a test module; the issue names no files or entry points. Define the initial functionality coverage and a repeatable test command, with passing tests establishing what is covered.

Written by the indexing model from the issue text.