Set up Jest/React Testing Library tests.

[ray-lee]

Description

This adds configuration needed to start writing tests using Jest and React Testing Library (instead of Mocha and Enzyme). Existing Mocha/Enzyme tests are unchanged. New Jest/RTL tests should be placed in the tests/jest directory. The npm test script now runs both the old Mocha/Enzyme tests as well as the new Jest/RTL tests.

Motivation and Context

The Enzyme test utility for React doesn't currently support React 17, and likely won't support React 18. In order to advance beyond React 16, we'll need an alternative for testing. The React team is recommending React Testing Library as a replacement. A common pattern for writing tests using React Testing Library is to mock components that are not under test using Jest's mock function, so Jest is included. While it's not necessary to use Jest as a test runner, mixing Mocha (as a test runner) and Jest (only for the mock function) would be confusing, so the new tests are configured to run using Jest.

Notion: https://www.notion.so/lyrasis/Set-up-React-Testing-Library-and-Jest-for-testing-in-admin-UI-ae75b457da19440a916b12a569dba289

How Has This Been Tested?

• npm install in a clean directory (no lib, no node_modules) should work.
• npm test should work.

Checklist:

• I have updated the documentation accordingly.
• All new and existing tests passed.

[tdilauro]

Looks good! 🚀