Question

171

Test callback function with jest

rated 0 times [ 172] [ 1] / answers: 1 / hits: 27153 / 5 Years ago, thu, may 2, 2019, 12:00:00

I'm trying to test a function with a callback inside. I set up a mock function, but I also need to test a callback.

I've tried to separate it as another mock function, but it doesn't counted as covered.

Function I'm trying to test:

export const checkDescription = async page => {

    const metaDescription = await page.$eval(

      'meta[name=description]',

      description => description.getAttribute(content)

    );

    return metaDescription;

};

I've mocked the page function :

const page = {

  $eval: jest.fn(() => Value)

};

my test :

test(Should return description, async () => {

  expect(await checkDescription(page)).toBe(Value); 

  expect(page.$eval).toHaveBeenCalled();

});

I've tried to separate description :

const description = {

  getAttribute: jest.fn(() => Value)

};

but I don't think that it's a correct way to cover description inside $eval.

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mckinley

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4 Years ago

answered 5 Years ago margaritakristinak · Accepted Answer

You're close!

The description arrow function is passed to your page.$eval mock function so you can use mockFn.mock.calls to retrieve it.

Once you've retrieved it, you can call it directly to test it and get full code coverage:

test(Should return description, async () => {

  expect(await checkDescription(page)).toBe(Value);  // Success!

  expect(page.$eval).toHaveBeenCalled();  // Success!



  const description = page.$eval.mock.calls[0][1];  // <= get the description arrow function

  const getAttributeMock = jest.fn(() => 'mock content');

  expect(description({ getAttribute: getAttributeMock })).toBe('mock content');  // Success!

  expect(getAttributeMock).toHaveBeenCalledWith('content');  // Success!

  // Success!  checkDescription now has full code coverage

});