I'm using Jest + Enzyme. I have a function,

     submitHandler = values => {
         return new Promise((resolve, _) => {
                saveSomething({values, resolve});
         }
     }

My test:

    it('Should call saveSomething on form submit', () => {
        const values = {firstName: 'FName', lastname: 'LName'};
        const {enzymeWrapper, props} = setup();
        enzymeWrapper.find('Formik').simulate('submit', values);
        expect(props.saveSomething).toBeCalledWith({
            values: {
                ...values,
                contactLanguage: LOCALE_TO_LANGUAGE_MAP[props.locale],
            },
        });
    });

Currently, my test is failed. Error:

    Error: expect(jest.fn()).toBeCalledWith(...expected)

    - Expected
    + Received

    @@ -1,6 +1,7 @@
      Object {
    +   "resolve": [Function anonymous],
        "values": Object {
          "contactLanguage": "FRENCH",
          "firstName": "FName",
          "lastname": "LName",
        },,

Question: How to mock resolve function?

I'm using Jest + Enzyme. I have a function,

     submitHandler = values => {
         return new Promise((resolve, _) => {
                saveSomething({values, resolve});
         }
     }

My test:

    it('Should call saveSomething on form submit', () => {
        const values = {firstName: 'FName', lastname: 'LName'};
        const {enzymeWrapper, props} = setup();
        enzymeWrapper.find('Formik').simulate('submit', values);
        expect(props.saveSomething).toBeCalledWith({
            values: {
                ...values,
                contactLanguage: LOCALE_TO_LANGUAGE_MAP[props.locale],
            },
        });
    });

Currently, my test is failed. Error:

    Error: expect(jest.fn()).toBeCalledWith(...expected)

    - Expected
    + Received

    @@ -1,6 +1,7 @@
      Object {
    +   "resolve": [Function anonymous],
        "values": Object {
          "contactLanguage": "FRENCH",
          "firstName": "FName",
          "lastname": "LName",
        },,

Question: How to mock resolve function?

• javascript
• unit-testing
• jestjs
• enzyme

• The code you gave is inplete – Lin Du Commented Apr 3, 2020 at 4:27
• @slideshowp2 what do you mean? – D.Mark Commented Apr 6, 2020 at 4:59

1 Answer 1

Jest mocks have an inherent method to cope with Promise resolutions and rejections. Please refer to the Jest Mock API for details.

The mockResolvedValue method is used for this very purpose.

Just mock your submitHandler with a simple call to jest.fn() and add the mockResolvedValue method.

You can test rejections as well with the mockRejectValue method.