9395 Set up basic Jest/Enzyme tests for React

[cooperka]

Closed in favor of #581

---

Fairly simple change overall, but you can read commit-by-commit if you want to see the process.

• Jest framework
• Enzyme toolkit
• Basic working snapshot test with component interaction
• Integrate with CI (@smoyth wanted to handle this)

[smoyte]

Super cool! Just one question about the babelrc thing. Thanks for teaching me about this stuff!

[cooperka]

@smoyth I think tests are failing now because some test suite isn't setting a NODE_ENV (or it's something other than test or production). Tests worked both before and after removing modules: false from the config, so it must be because of the env change.

Can you point me to the command that runs the test that gave this output on CI:

------------ BROWSER LOGS -------------
SEVERE 2019-02-15 17:48:45 +0000: http://127.0.0.1:44746/packs-test/application-d44347d2ad8823ff9d55.js 23362:16 Error: Module build failed: SyntaxError: Unexpected token (20:6)
  18 |     const displayIfOptions = ["always", "all_met", "any_met"];
  19 |     return displayIfOptions.map((option) => (
> 20 |       <option
     |       ^