Investigate testing for sharing functionality

[MatthewGidcomb]

Today we discovered that:

• The share to Facebook and Twitter functionality was broken, because
  • The computed property that generated the link for FB was incorrectly using the API URL instead of the portal, and
  • The Twitter link was hard-coded to use the Bitly link, which we've stopped generating
• Sharing using built-in functionality on iPhone (and probably Android) was broken because we generated a broken canonical link in the head.

These problems are fixed by #323 and 668d4b9a. But we should think about how we might test these going forward.

[MatthewGidcomb]

Some thoughts to start off:

• We could add a Cypress test, or augment an existing one, to look at the event view, click the button to activate the "Share" dropdown, and verify that the href of the FB and Twitter links contain the proper URL. I wouldn't want to test the full "share" URL, e.g. https://<evilempire>.com/<some-sharing-thing>?url=<infinite>, but if the string contained http://localhost:7779/events/uuid-..., I think we could be confident everything works.
• Similarly, we could also look for elements in the head to verify the canonical URL, and there might be other things in the head we want to verify.
• Alternatively (or in combination with the above), we could try to get a unit test going for the EventView component (that covers most of the page content for the /events/uuid... page) that verifies these links given a test event. I don't know if the head content could be testing, though.