Jest throws TypeError: (0 , _module.myFunction) is not a function, testing exported functions (non default) with Jest

user_4031815 0
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So I'm using Jest, Typescript and Create-react-app

I have this test:

import { defaultHeaders } from './http';

describe('http tests', () => {
  test('defaultHeaders()', () => {
    const headers = defaultHeaders(undefined);
    expect(headers).toEqual({ foo: 2 });
  });
});

The code is in same subdir in file http.ts and looks like this:

export function defaultHeaders(headers?: FetchHeaders): FetchHeaders {
  return { 'Content-Type': 'application/json' };
}

When I run my jest tests it throws:

TypeError: (0 , _http.defaultHeaders) is not a function

The weird part is that all other tests that are wrapped in a default function or const do work.

Is there any way to test non default exported functions with Jest?

update:

  • also tried converting defaultHeaders into an arrow function and that didn't help.
  • and tried changing import as: import * as http from './http' that still makes it throw same error
create-react-app jestjs typescript
1 Answers

Update with Answer

So the issue was that in src/setupTest.ts I included a mock of the module without the function I was trying to test therefore it was undefined.

// mock our fetch wrapper to avoid doing http calls in tests
jest.mock('utilities/http/http', () => ({
  // NO defaultHeaders() function mocked that was the problem 
  getRequest: function () {
    return {
      json: {},
      status: 200,
    };
  },
  postRequest: function () {
    return {
      json: {},
      status: 200,
    };
  },
  request: function () {
    return {
      json: {},
      status: 200,
    };
  },
}));

If I remove the mocked from setupTest.ts then I can unit test it.

user_40318150
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