test: add testing with jest

[ejfox]

So this is mostly set up except this very simple test is failing:

// TODO: This times out for some reason I do not understand
test('get NY state code from county fips', (t) => {
  const helperStateCode = helpers.getStateCodeFromCountyFips('36001')
  expect(helperStateCode).toBe('36')
})

~/code/election-helpers  master [!?⇡] is 📦 v0.0.2 ⬢ v16.13.2 // 21s 
✗  npm run test                                                             [git:master] ✖  

> election-helpers@0.0.2 test
> node --experimental-vm-modules node_modules/.bin/jest --runInBand

(node:96938) ExperimentalWarning: VM Modules is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
  console.log
    36

      at Object.<anonymous> (index.test.js:8:11)

 FAIL  ./index.test.js (20.175 s)
  ✕ get NY state code from county fips (20001 ms)

  ● get NY state code from county fips

    thrown: "Exceeded timeout of 20000 ms for a test.
    Use jest.setTimeout(newTimeout) to increase the timeout value, if this is a long-running test."

       5 | // console.log(helpers)
       6 |
    >  7 | test('get NY state code from county fips', (t) => {
         | ^
       8 |   const helperStateCode = helpers.getStateCodeFromCountyFips('36001')
       9 |   expect(helperStateCode).toBe('36')
      10 | })

      at index.test.js:7:1
      at TestScheduler.scheduleTests (node_modules/@jest/core/build/TestScheduler.js:317:13)
      at runJest (node_modules/@jest/core/build/runJest.js:407:19)
      at _run10000 (node_modules/@jest/core/build/cli/index.js:339:7)

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total
Snapshots:   0 total
Time:        20.21 s, estimated 21 s
Ran all test suites.