Getting `TypeError: jest.fn is not a function`

Question

I'm trying to create the following unit test using Jest.

jest.dontMock("pointsAwardingActions.js");
describe("points awarding actions", () => {
  describe("award points", () => {
    it("should dispatch begin ajax action", () => {
      var pointsAwardingActions = require("pointsAwardingActions.js");
      const mockedDispatch = jest.fn();
    });
  });
});

But I'm getting the following error after running npm test.

TypeError: jest.fn is not a function

This is some section of my package.json:

{
  "scripts": {
    "test": "jest"
  },
  "author": "alayor",
  "license": "ISC",
  "jest": {
    "scriptPreprocessor": "<rootDir>/node_modules/babel-jest",
    "testFileExtensions": ["spec.js"],
    "moduleFileExtensions": ["js"],
    "collectCoverage": "true"
  },
  "dependencies": {
    "babel-cli": "6.8.0",
    "babel-core": "6.8.0",
    "babel-jest": "^6.0.1",
    "babel-loader": "6.2.4",
    "babel-plugin-react-display-name": "2.0.0",
    "babel-polyfill": "6.8.0",
    "babel-preset-es2015": "6.6.0",
    "babel-preset-react": "6.5.0",
    "babel-preset-react-hmre": "1.1.1",
    "expect": "1.19.0",
    "express": "4.13.4",
    "jest": "^0.1.40",
    "jest-cli": "^0.8.1",
    ...
  }
}

What could be the reason I'm getting that error?

score 30 · Accepted Answer · edited Oct 13 '20 at 20:14

30

The jest object is automatically in scope within every test file, so there's no need to import it explicitly. If you do want to import the jest object directly, you want to import the jest-mock module, not the jest-cli module, via:

// Not necessary inside a Jest test file
import jest from 'jest-mock';

const mock = jest.fn();

edited Oct 13 '20 at 20:14

Peter Mortensen

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answered Feb 25 '18 at 19:40

Rick Hanlon II

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this is what i looking for, this solve spyOn is not a function, also fn is not a function – elporfirio Apr 02 '19 at 18:10
1

I'm new to redux and jest and i can't describe the number of hours searching for this. You saved my life man – laserany Nov 27 '20 at 13:35

score 6 · Answer 2 · answered Feb 25 '18 at 18:14

6

It is a bit weird that documentation isn't mentioning that jest is not require('jest'); but require('jest-mock'), the following code should work on v22:

const jest = require('jest-mock');
const spy = jest.fn();

answered Feb 25 '18 at 18:14

Anatoliy

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2

"The jest object is automatically in scope within every test file." https://facebook.github.io/jest/docs/en/jest-object.html – Rick Hanlon II Feb 25 '18 at 19:36
@RickHanlonII Every test file... but not files in __mocks__ directories. – Tin Wizard Aug 21 '18 at 00:37
Another situation this is useful: playing on Node's console, you need to require it specifically – Manu Artero Feb 18 '21 at 14:25

score 3 · Answer 3 · edited Mar 27 '18 at 06:42

3

You’re using a very old version of Jest that don’t support jest.fn. Jest has significantly improved since then and I highly recommend you to update to the latest version.

Also they don’t do auto mocking now.

edited Mar 27 '18 at 06:42

Anima-t3d

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answered Sep 08 '17 at 07:11

Artem Sapegin

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@TFischer did you try the answer by Rick? https://stackoverflow.com/a/48977663/3163075 – Anima-t3d Mar 27 '18 at 05:44

score -1 · Answer 4 · edited Oct 13 '20 at 20:15

-1

It's already included in your Jest package, so please make sure that you type correct like this: ("mockReturnValue").

It will clear your error.

edited Oct 13 '20 at 20:15

Peter Mortensen

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answered May 28 '20 at 13:01

Nirakar

1

Getting `TypeError: jest.fn is not a function`

4 Answers4

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