Question

115

asserting against thrown error objects in jest

rated 0 times [ 116] [ 1] / answers: 1 / hits: 36077 / 6 Years ago, fri, february 9, 2018, 12:00:00

I have a function which throws an object, how can I assert that the correct object is thrown in jest?

it('should throw', () => {



  const errorObj = {

    myError: {

      name: 'myError',

      desc: 'myDescription'

    }

  };



  const fn = () => {

    throw errorObj;

  }



  expect(() => fn()).toThrowError(errorObj);

});

https://repl.it/repls/FrayedViolentBoa

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aidengiancarlop

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4 Years ago

answered 6 Years ago margaritakristinak · Accepted Answer

If you are looking to test the contents of a custom error (which I think is what you are trying to do). You could catch the error then perform an assertion afterwards.

it('should throw', () => {

 let thrownError;



 try {

   fn();

 }

 catch(error) {

  thrownError = error;

 }



 expect(thrownError).toEqual(expectedErrorObj);

});

As Dez has suggested the toThrowError function will not work if you do not throw an instance of a javascript Error object. However, you could create your custom error by decorating an instance of an error object.

e.g.

let myError = new Error('some message');

myError.data = { name: 'myError',

                 desc: 'myDescription' };

throw myError;

Then once you had caught the error in your test you could test the custom contents of the error.

expect(thrownError.data).toEqual({ name: 'myError',

                                   desc: 'myDescription' });