How to use jest flow-types in tests

After running flow-typed install and getting package flow-typed/npm/jest_v21.x.x.js, how are we supposed to use these types? The names that flow check requires are not resolving

For example, this fails with the following messages: Missing type annotation for TArguments AND Cannot resolve name TArguments

export const fn = jest.fn(...args: TArguments): TReturn => {
    ...
};

Here’s an untyped boilerplate example of what I am having issues with:

// @flow
// fetch mock
export const fn = jest.fn(() => (url, params) => {
  console.log(params);
  console.log(url);
  return new Promise(resolve => resolve({ ok: true, status: 200 }));
});

export default jest.mock('../../src/shared/fetch', fn);

And here are the errors flow is giving me:

Error ------------------------------------------------------------------------------------------------- untitled.js:3:19

Missing type annotation for `TArguments`.

                        v-------------------------------
   3| export const fn = jest.fn(() => (url, params) => {
   4|   console.log(params);
   5|   console.log(url);
   6|   return new Promise(resolve => resolve({ ok: true, status: 200 }));
   7| });
      -^


Error ------------------------------------------------------------------------------------------------- untitled.js:3:19

Missing type annotation for `TReturn`.

                        v-------------------------------
   3| export const fn = jest.fn(() => (url, params) => {
   4|   console.log(params);
   5|   console.log(url);
   6|   return new Promise(resolve => resolve({ ok: true, status: 200 }));
   7| });
      -^

[cortopy]

@sobolevn solution doesn’t work for me

I’m getting babel parser errors: “Unexpected token”

My babel config:

"babel": {
    "presets": [
      "flow",
      [
        "env",
        {
          "targets": {
            "node": "8.10.0"
          }
        }
      ]
    ]
  },

[thejettdurham]

@cortopy I had the same parsing error as you when using the provided example, but was able to move the type annotations to the left-hand-side of the assignment to get a version that worked 🙂

export const mockFn: ($ReadOnlyArray<string>) => string = jest.fn();