CODEWITHSUNDEEP
javascriptreactjsunit-testingjestjs
user1177227
user1177227

Reputation: 97

Mock function with jest that contains a callback as an argument which returns a promise

I'm integrating with a 3rd party script and have come across a scenario which I don't know how to test properly.

The 3rd party script adds an object to the window with a few methods. The second argument of the create method is a callback function which returns a promise that is either rejected or resolved.

I need to be able to mock that second argument with either a reject or resolved status so that my unit test can cover whether the UI is updated with either the error or success message.

How can I mock this function and the callback function with the proper response?

thirdpartyform.create(options, (err, message) => {
  return new Promise((resolve, reject) => {
    if (err) {
      reject(err.reason)
    } else {
      resolve(message)
    }
  })
  .then(message => {
    setState(message)
  })
  .catch((err) => {
    setState(err)
  })
})

Below is my current attempt at mocking the function (against the window object) which is not working. It does not properly set the rejected value or resolved value :(

create: jest.fn((options, callback) => callback(jest.fn().mockRejectedValue(FORM_TIMEOUT)))

Any help would be greatly appreciated

Upvotes: 2

Views: 2403

Answers (1)

Estus Flask
Estus Flask

Reputation: 222493

create is callback-based and is unaware of promises, so a mock shouldn't involve promises either.

Given that thirdpartyform.create is a spy that has been previously set up with jest.mock, jest.spyOn, etc, a mock for successful response:

thirdpartyform.create.mockImplementation((options, cb) => cb(null, 'message'))

A mock for unsuccessful response:

thirdpartyform.create.mockImplementation((options, cb) => cb({ reason: 'error' }))

Upvotes: 3

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