JEST - check if objects array is a subset of another array

Question

Using JEST I want to test if an array of objects is a subset of another array.

I want to test the following:

const users = [{id: 1, name: 'Hugo'}, {id: 2, name: 'Francesco'}, {id: 3, name: 'Carlo'}];
const subset = [{id: 1, name: 'Hugo'}, {id: 2, name: 'Francesco'}];

expect(users).toContain(subset)

I've tried the following:

describe('test 1', () => {
  it('test 1', () => {
    expect(users).toEqual(
      expect.arrayContaining([
        expect.objectContaining(subset)
      ])
    )
  });
});

But this is not correct since objectContaining doesn't accept array as param ... it works only if subset is a single object.

instanceof · Accepted Answer · 2022-04-11 08:49:38Z

4

I've never tried this myself, but wouldn't it work to just say:

expect(users).toEqual(
  expect.arrayContaining(subset)
)

answered Apr 11, 2022 at 8:49

instanceof

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Comments

Mr.7 · Accepted Answer · 2023-07-18 07:36:33Z

You were almost there.. but this line was causing you the trouble expect.objectContaining(subset) where you are supposed to pass an object instead of an array.

As @instanceof mentioned, below code would work.. but let me share the details like what's happening here

expect(users).toEqual(
    expect.arrayContaining(subset)
)

In the above snippet, expect.arrayContaining(subset) matches a received array which contains all of the elements in the expected array. That is, the expected array is a subset of the received array.

Please note that even if you are checking for a single element, you need to pass it as an array to arrayContaining() method

Same applies for objectContaining() as well.. let's say if you want to check an Array contains an object, you can test it something like this

expect(users).toEqual(
    expect.arrayContaining([ // Note that it should be an array
        expect.objectContaining({ // Note that it should be an object
            id: 123,
        });
    ]);
);

Hope this helps :)

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