Address new eslint issues in tests

[sprucely]

After CRA is upgraded to 5.0.1 (#862), there will be some new eslint warnings that will need some work.

• Avoid wrapping Testing Library util calls in 'act'
  Rendering of react components shouldn't be wrapped in act call. Instead, wrap the subsequent code in waitFor from @testing-library/react, ie: await waitfor(() => { ... })

• Avoid direct Node access. Prefer using the methods from Testing Library.
  Eliminate the usage of a manually created document and container element, and use the render function from @testing-library/react instead of react-dom

  Replace container.querySelector with equivalent getBy... functions on screen from @testing-library/react. There is no equivalent for css class selectors, so an alternative will need to be found for identifying those elements.

After those are addressed, I don't know if more issues will crop up. Eslint doesn't seem too keen on showing all classes of issues at once.