What's the right way to write Jest tests verified with Flow?

Question

I imagine people commonly use Flow and Jest (and React) together, but Flow doesn't seem to know about Jest (or Jasmine) globals. When I add // @flow to my tests, I get Flow errors like this:

src/__tests__/Thing-test.js:3
  3: jest.unmock('../Thing')
     ^^^^ identifier `jest`. Could not resolve name

src/__tests__/Thing-test.js:7
  7: describe('Thing', () => {
     ^^^^^^^^ identifier `describe`. Could not resolve name

src/__tests__/Thing-test.js:8
  8:   it('does stuff', () => {
       ^^ identifier `it`. Could not resolve name

I could write a Flow interface for Jest/Jasmine, but that seems lengthy and like I must be missing something. Letting Flow process node_modules/jest-cli doesn't seem to help.

Answer 1

Although Jest is written with flow annotations they strip types for the npm version so we don't need babel to run it. Fortunately the types are already in flow-type so the solution is quite easy (just as mentioned in the comment):

npm install -g flow-typed

flow-typed install [email protected] # <-- replace the version with the latest

Although I had to add this line as well to my .eslintrc.json:

{
  "env": {
    "jest": true
  }
}