Feature Request: Add linting checks and unit tests to repo

[tgrowden]

@techniq When working on #48, I noticed a couple of things that I thought could improve the repo:

• You have a .eslintrc, but there's no lint script in package.json, nor is any linting being done via CI. Several lint errors have made their way into the codebase.
• There are no unit tests.

If you think adding these features would be beneficial, I'd be happy to get the ball rolling.

[techniq]

@tgrowden That would be great. In my visual repos I've typically just leverage react-storybook but it doesn't catch visual regressions, etc (without manual testing, etc).

For my other repos, my testing stack is typically jest with react-testing-library, and I'll use fetch-mock if I need to mock out some requests. You can see my setup for another project here.

I wouldn't mind adding prettier as part of the workflow as well (I run it locally on save, but it would be nice to have it ran on git stage, etc). Something like this.

As always, any help is very much appreciated. I've been working on a big update for mui-table this weekend and typically my open source is driven by my need in private projects, but I like to open source / support what I can.