Jest compare object with arbitrary property value

Question

I'm testing rest API with Jest. I know we use toEqual to check whether two objects are equal or not by recursively compare all the properties.

For primitive values toEqual uses Object.is for the comparison.

Problem

The problem I'm having is while testing /register endpoint. After once a user successfully registered, the endpoint returns the user details. Use details contain information like phone, name, email, and what is more important in this case a user_id.

Now, what I'm trying is like this:

const data = {
  sponsor_id: 'ROOT_SPONSOR_ID',
  phone: '9999999999',
  name: 'Joe',
  password: 'shhhhh'
};

// Some API call goes here which returns `body`

expect(body).toEqual({
  user_id, // <-- How to test value of this?
  sponsor_id: data.sponsor_id,
  phone: data.phone,
  name: data.name
});

I don't know beforehand what would be the returned value of user_id field. All I know that it would be a Number. Now it can be any numeric value so how to test an object property with any value or any numeric value in this case?

One thing that I also wanted to check that I'm sending any extra data (properties) than what I'm expecting. Which by the way using toEqual is taking care of already.

If my approach of the way I'm testing this is flawed then please provide me with a better one with some explanation.

Answer 1

Use expect.any(Number) to ensure that user_id is a Number:

test('matches', () => {

  const data = {
    sponsor_id: 'ROOT_SPONSOR_ID',
    phone: '9999999999',
    name: 'Joe',
    password: 'shhhhh'
  };

  const user_id = Math.floor(Math.random() * 1000);
  const body = Object.assign(data, { user_id });

  expect(body).toEqual({
    user_id: expect.any(Number),  // user_id must be a Number
    sponsor_id: data.sponsor_id,
    phone: data.phone,
    name: data.name,
    password: data.password
  });  // SUCCESS

});

---

Note that if you want an even more specific matcher you can create your own using expect.extends.