Add test page and test of test page

[dbjorge]

Description of changes

Sets up a test of a static page using selenium-webdriver

• Adds a test page at src/index.html
• Adds a test of it at tests/index.test.ts
• Removes placeholder tests
• Adds a yarn serve (I wanted it for testing purposes but thought it might be nice to keep)
• Works around Jest is using stderr as output jestjs/jest#5064

Pull request checklist

• Addresses an existing issue: n/a
• Added relevant unit test for your changes. (yarn test)
• Verified code coverage for the changes made.

[dbjorge]

Closing and reopening to retrigger pipelines