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

问题:

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.

回答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  # replace the version with the jest version in your package.json flow-typed install jest@22.x.x 

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

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

回答2:

If you created your project with create-react-app you have to manually add jest to your packages.json. Otherwise flow-typed won't install the needed type definitions because create-react-app doesn't add this dependency to packages.json.

yarn add --dev jest flow-typed install 

回答3:

I think declare var jest: any; should do the trick (put it either on top of each test file, or somewhere in your flow lib directory).

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