expect.toMatchObject throws TypeError instead of showing diff

[heygent]

🐛 Bug Report

expect.toMatchObject throws a TypeError when an object A is expected to match an object B, where A has been created with Object.create(null) and B has properties that aren't in A.

To Reproduce

it('should work with Object.create(null) objects', () => {
  const obj = Object.assign(
    Object.create(null),
    { hello: 'world' }
  );

  expect(obj).toMatchObject({
    hello: 'world',
    foo: 'bar'
  });
});

Output:

 FAIL  ./add-test.js
  ✕ should work with Object.create(null) objects (11ms)

  ● should work with Object.create(null) objects

    TypeError: Cannot read property 'prototype' of undefined

       5 |   );
       6 | 
    >  7 |   expect(obj).toMatchObject({
       8 |     hello: 'world',
       9 |     foo: 'bar'
      10 |   });
      
      at Object.<anonymous>.it (add-test.js:7:15)

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total
Snapshots:   0 total
Time:        0.834s, estimated 1s
Ran all test suites.

Expected behavior

The test should fail and show the diff between the objects.

Link to repl or repo (highly encouraged)

https://repl.it/repls/SizzlingWoodenAcrobat

[shai32]

I did some debugging, it fails here

object it the object inside expect,
and its object.constructor is undefined

[richardgirges]

Been running into this issue for a while. It took me a while to realize that this TypeError is only thrown when the objects don't match. Makes a lot more sense now that I'm looking at @shai32's findings.

[SimenB]

A PR fixing this is most welcome!

[github-actions]

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