Jest - one function mocks file for multiple test files

Question

I want to have something like this:

mockFunctions.ts

jest.mock('../utils', () => {
  return {
     getNumbers: () => [1,2,3]
  }
})

__tests__/test1.ts

---import from mockFunctions---
...
it('After adding another number array has more elements', () => {
   const numbers = <get these numbers using mock function>
   expect([...numbers, 11]).toHaveLength(4);
})

__tests__/test2.ts

---import from mockFunctions---
...
it('After removing a number, array has less elements', () => {
   const numbers = <get these numbers using mock function>
   expect(numbers.filter(x => x>1)).toHaveLength(2);
})

Is it possible to have one file where mocked functions are implemented, and then import them in multiple tests files?

Answer 1

There are some alternative to accomplish this:

1. Add __mocks__ directory inside utils folder. See https://jestjs.io/docs/en/manual-mocks

utils/index.js

export const  getNumbers= () => [1, 2, 3, 4, 5];

->utils/ __mocks__ /index.js

export const  getNumbers= () => [3, 4];

jest.config.js

{ 
   "setupFilesAfterEnv": [
      "<rootDir>/jestSetup.js"
    ]
}

jestSetup.js

jest.mock("../utils"); // will apply to all tests

2. Add mock definition directly in jestSetup.js

jest.config.js

{ 
   "setupFilesAfterEnv": [
      "<rootDir>/jestSetup.js"
    ]
}

jestSetup.js

  jest.mock("../utils", () => ({
     getNumbers: () => [3, 4]
  }));

or create a file with mocks

mocks.js

  jest.mock("../utils", () => ({
     getNumbers: () => [3, 4]
  }));

jestSetup.js

  import './mocks.js'

If you don't want to use mocks on specific test, you can call:

jest.unmock('../utils')

See: https://jestjs.io/docs/en/jest-object#jestunmockmodulename