Jest passing an object to expect().toBeCalledWith()

Question

I'm using jest to test my react components and I'm using expect(...).toBeCalledWith(...); to test if a function has been called with specific parameters, and it works fine with value types.

The problem is I want to test a function that takes object as a parameter so when you call expect(myFunc).toBeCalledWith(object); the test always fails because of course the two object compared to each other do not have the same reference.

so how can I solve this problem ?

a sample code of what I'm trying to test is

it('the function should be called with the correct object', () => {
    api.submitForm = jest.fn().mockReturnValue(Promise.resolve());
    const wrapper = shallow(<component />);
    const instance = wrapper.instance();
    instance.submitForm();
    const object = {
      foo : 'foo',
      bar: 'bar'
    };
    // this always fails even the function is called with the same object values
    expect(api.submitForm).toBeCalledWith(object);
  });

An error message would be something like this

Expected mock function to have been called with:
      [{"bar": "bar", "foo": "foo"}]
    But it was called with:
      [{"bar": "bar", "foo": "foo"}]

Update

it seems the below code works fine

  expect(api.submitForm).toBeCalledWith(
    expect.objectContaining({
     foo : 'foo',
      bar: 'bar'
    }),
  );

however, if the object contains a property with array value, the above solution doesn't work

const obj = {
  foo : ['foo1', 'foo2'],
  bar: 'bar'
}

The problem could be something else. I have used the above pattern in my code and it works as expected — Pubudu Dodangoda, Dec 23 '17 at 14:39
The jest doc itself at here shows that they are comparing the value, not the reference, https://facebook.github.io/jest/docs/en/expect.html#tohavebeencalledwitharg1-arg2- — Pubudu Dodangoda, Dec 23 '17 at 14:50
I'm using jest `20.0.4`, and the problem happens if you have an array property in your object — Nader Hisham, Dec 23 '17 at 15:02
the second solution works now I've discovered a typo in my code. — Nader Hisham, Dec 23 '17 at 15:06

score 91 · Accepted Answer · edited Apr 25 '23 at 17:18

91

Looking at the jest doc (https://jestjs.io/docs/expect#expectobjectcontainingobject). It seems you can do something like this:

 expect(api.submitForm).toBeCalledWith(
    expect.objectContaining({
     foo : 'foo',
      bar: 'bar'
    }),
  );

edited Apr 25 '23 at 17:18

Matt_Bro

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answered Dec 23 '17 at 14:38

Kevin Amiranoff

13,440
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90

This would work. But the real intention of expect.objectContaining is slightly different – Pubudu Dodangoda Dec 23 '17 at 14:43
8

this works fine actually, but the problem if your object contains an array property – Nader Hisham Dec 23 '17 at 15:00
Man I love good documentation! Thanks [jest] team! – tim.rohrer May 02 '22 at 20:59
This doesn't work if being expected object contains a object in itself, and we need to match on this nested object property. What can be done in this case? Ex {headers:{a:10},z:20} need to match on "a" equals 10 – Nandan Raj Mar 09 '23 at 10:35

score 8 · Answer 2 · answered May 04 '22 at 22:01

you can use .mock.calls[callIdx][paramIdx]
description + example: https://stackoverflow.com/a/41939921/2519073

in your case

expect(api.submitForm.mock.calls[0][0]).toMatchObject( // use whatever matcher you want
    {
      foo : ['foo1', 'foo2'],
      bar: 'bar'
    },
  );

vanduc1102 · Answer 3 · 2022-05-09T01:19:42.147

3

In case you your function is called with arguments

function update( userId, partialUserObject ){
   // update logic
}

You can use

expect(update).toBeCalledWith('mockUserId',
   expect.objectContaining({
     username:'hello-world',
     displayName: 'Hello World'
   })
);

edited May 09 '22 at 01:19

answered Aug 30 '21 at 06:29

vanduc1102

5,769
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Jest passing an object to expect().toBeCalledWith()

Update

3 Answers3