Mock jwt-decode in Jest

Question

For test purposes I need to mock jwt-decode library. I use it as follows:

const decodedToken: { exp: number } = jwt_decode(token);

And then in tests tried the following and got errors like below:

jest.mock('jwt-decode');

TypeError: Cannot read property 'exp' of undefined

jest.mock('jwt-decode', () => ({
  exp: 123,
}));

TypeError: (0 , _jwtDecode.default) is not a function

Related to https://stackoverflow.com/q/47056694/7470360 (but I don't think it's a duplicate). — A Jar of Clay, Feb 26 '20 at 12:58

score 17 · Accepted Answer · answered Feb 25 '20 at 15:51

17

The issue is with the second argument of jest.mock. In your example, it is a function that returns an object:

jest.mock('jwt-decode', () => ({ ... }))

but as the property you are trying to mock is the default export of the module, the argument needs to be a function that returns a function that returns an object:

jest.mock('jwt-decode', () => () => ({ ... }))

answered Feb 25 '20 at 15:51

A Jar of Clay

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I had to do `jest.mock('jwt-decode', () => ({ default: () => ({ ... }) }))`. – zbr Feb 15 '22 at 11:25
Thanks @zbr It has worked for me nicely. – Rakib Feb 15 '22 at 20:16
How do i return different return values in different specs? I have tried ``` const jwt = jest.mocked(jwtDecode) await jwt.mockImplementationOnce(() => result)``` but this doesn't seem to work – user1801879 Mar 15 '23 at 08:36
@user1801879 see https://stackoverflow.com/q/45006254/7470360. Does that help? – A Jar of Clay Mar 17 '23 at 16:19
@AJarofClay i was able to use chatgpt to find an answer and it had worked – user1801879 Mar 23 '23 at 01:03

Mock jwt-decode in Jest

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