Feature/react tests

[nbarlowATI]

Very minimal set of tests for react components, essentially just verifying that each major component will render. Some notes:

• The mermaid chart doesn't seem to render for some reason- the page says "Syntax error in graph", so we test for that
• ItemViewer test hangs forever if we have an async waitFor around the expect, so we remove that.
• In several cases (e.g. ItemViewer), not clear why getByText doesn't find text element. getByPlaceholderText seems to be a reliable way of finding placeholder text in forms though.

Related to #20 (see that issue for more detailed discussion of issues.)
More detailed and useful tests to be added in the future, but probably worth merging this skeleton into main for now.

[coveralls]

Pull Request Test Coverage Report for Build 2022853977

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-2.6%) to 86.909%

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Totals
Change from base Build 2005252339:	-2.6%
Covered Lines:	1434
Relevant Lines:	1650

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💛 - Coveralls

[mhauru]

Looks great, just had a few questions that are mostly about me understanding what is going on.