Add tests

[maxxcrawford]

Summary:

• Added tests retroactively to the project.
• Using Jest testing framework

PR Goals:

• Modify code as little as possible
• Avoid adding build process
• Determine and account for code coverage

TODO:

• [ ] Add CircleCI Config
• [ ] Pass linters
• [ ] Add mock browser to confirm popup Notification UI

[maxxcrawford]

@jonathanKingston Please give review – I plan on adding additional tests before merging but wanted to get a gut check on current progress.