Need unit tests

[dmitrizzle]

Bug or feature request?

feature

chat-bubble is a simple, vanilla-JS app written in ES5. It's been thoroughly tested in production and has been delivering stable experience to its users for years. However, I would like to see some integration tests to ensure that this code continues to be stable for many more years.

I recommend jest via github-actions.

The only downside is that we'll have to have dev-dependencies which will have no effect on production versions of the app but will require additional maintenance from the developers.