I've been using Jest in a small project, and am having trouble with Jest mocks. I have a utility file that exports named custom error constructor functions. I need to mock those functions in my test file. I don't want to use the manual mocking technique shown in the Jest documentation (i.e., putting a mock file in __mocks__), but rather I want to define the mocks in the test file. I am trying something like this in my test file:

const errorMock = () => {
  return {
    configNotFoundError: jest.fn(() => new Error()),
    invalidJSONError: () => jest.fn(() => new Error()),
  }
};

jest.mock('./error', errorMock);

const { configNotFoundError, invalidJSONError } = require('./error');

But I get the following error:

babel-plugin-jest-hoist: The second argument of `jest.mock` 
must be an inline function.

Could someone help me understand what I'm doing wrong?

I've been using Jest in a small project, and am having trouble with Jest mocks. I have a utility file that exports named custom error constructor functions. I need to mock those functions in my test file. I don't want to use the manual mocking technique shown in the Jest documentation (i.e., putting a mock file in __mocks__), but rather I want to define the mocks in the test file. I am trying something like this in my test file:

const errorMock = () => {
  return {
    configNotFoundError: jest.fn(() => new Error()),
    invalidJSONError: () => jest.fn(() => new Error()),
  }
};

jest.mock('./error', errorMock);

const { configNotFoundError, invalidJSONError } = require('./error');

But I get the following error:

babel-plugin-jest-hoist: The second argument of `jest.mock` 
must be an inline function.

Could someone help me understand what I'm doing wrong?

• javascript
• node.js
• unit-testing
• jestjs
• babel-jest

1 Answer 1

I had a similar problem with named exports recently. according to the docs, jest.mock calls are hoisted to the top of the test and are subsequently executed before you define errorMock. Functions seem to be hoisted above these calls. Try:

function errorMock() {
  return {
    configNotFoundError: jest.fn(() => new Error()),
    invalidJSONError: () => jest.fn(() => new Error()),
  }
};

jest.mock('./error', errorMock);

const { configNotFoundError, invalidJSONError } = require('./error');