Add unit tests for App component

[akmadian]

Fixes

Fixes #124 by @akmadian

Description

This PR adds unit tests for the App component. I didn't include any e2e tests because there's really no interactivity with the App component itself.

I couldn't think of many test cases so what I've got now feels somewhat anemic. Please let me know if you can think of any other cases and I'll implement them!

Tests

Run npm run test

Checklist

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• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[obulat]

This is great, merging, @akmadian.