rejects.toMatchObject(new Error(...)) always passes

[dandv]

Can't post a repl.it because it doesn't run Jest v20+, so here's the code using Promises and rejecting with Error objects (a recommended pattern).

function foo() {
  return new Promise(function (resolve, reject) {
    reject(new Error('bar'));
  });
}

test('rejection 1', () => {
  expect.assertions(1);
  return expect(foo()).rejects.toMatchObject(new Error('totally different'));  // passes!
});

I would expect the test above to fail.

It would also be nice to document how to test for rejection with specific error messages. return expect(foo()).rejects.toEqual('bar'); errors out:

expect(received).toEqual(expected)
    
Expected value to equal:
  "bar"
Received:
  [Error: bar]

Difference:

  Comparing two different types of values. Expected string but received object.

This works:

return expect(foo()).rejects.toEqual(new Error('bar'));

but the Note at the end of the toEqual(value) docs recommends against using it for Error objects and toEqual can be too strict when ideally you'd check for a Regexp.

[thymikee]

You can use toEqual to test Errors if that works for you.
However what this issue shows is that toMatchObject is not checking if the object is error, which can lead to hard-to-track bugs, like this one.
Example can be shortened to:

test('toMatchObject passes on different Errors', () => {
  expect(new Error('foo')).toMatchObject(new Error('bar'));
});

I'll close this and open new issue just for toMatchObject.

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