Identify functional testing approach for author selection component

The underlying component(s) that we use for the author selection control on the post editing screen will hopefully be tested, but it would be great to have functional tests in place to ensure it actually works in the context of where we use it (the block editor in #7 and the classic editor in #13). Suggestions for testing approach and framework welcome.

## Options

* [Jest React snapshot testing](https://jestjs.io/docs/en/tutorial-react)
* [Jest with Puppeteer](https://blog.logrocket.com/end-to-end-testing-react-apps-with-puppeteer-and-jest-ce2f414b4fd7/)
* [QA Wolf](https://github.com/qawolf/qawolf)
* [Something with the Gutenberg E2E test utils](https://developer.wordpress.org/block-editor/packages/packages-e2e-test-utils/) and [example usage here](https://github.com/liip/e2e-tests-example-wp-plugin)