Jest expect matcher extension for asserting whether the received object has only the properties specified via a list to the matcher

example.spec.js

test('received response only exposes the public fields', () => {
  const res = await request
    .post('/items')
    .send(newItem)
    .expect(status.CREATED);
  
  expect(res.body).toOnlyHaveProperties(["id", "name", "color"]);
});

test('returned object is extended', () => {
  const ret = addAnotherProp({a: 1, b: 2});
  
  expect(ret).not.toOnlyHaveProperties(["a", "b"]);
});

jest.setup.js

// see https://jestjs.io/docs/expect#expectextendmatchers
expect.extend({
  function toOnlyHaveProperties(received, allowedProps) {
    const receivedProps = Object.keys(received);
    const pass = JSON.stringify(receivedProps.sort()) === JSON.stringify(allowedProps.sort());
    if (pass) {
      return {
        message: () =>
          `expected ${received} to not only have properties ${JSON.stringify(allowedProps)}`,
        pass: true,
      };
    } else {
      return {
        message: () =>
          `expected ${received} to only have properties ${JSON.stringify(allowedProps)}`,
        pass: false,
      };
    }
  }
});