Add unit testing

[ptgott]

The legacy docs engine includes a unit test suite, which it runs using the following command:

loadr -- uvu uvu-tests

There hasn't been any development on loadr or uvu in a few years, so we should switch to an industry standard like Jest.

I propose we:

• Copy the test suite from gravitational/docs
• Convert the tests to use the Jest syntax
• Get the tests to pass
• Add a workflow to require the tests to pass on changes to docs-website

[ptgott]

We can also consider adding the Storybook tests from gravitational/docs, adapt them to the new website, and run them with Jest as part of the test workflow.

[taraspos]

@ptgott Amplify supports running cypress tests to run before deploying changes¹. Might be good to add at least some sanity check to make sure application loads as expected.

Footnotes

1. https://docs.aws.amazon.com/amplify/latest/userguide/running-tests.html ↩