Mocha.utils.stringify() hangs on recursive data structures

[oleg-codaio]

I'm using Chai, and often use assert.deepEqual() to make sure that one object is equal to another. This works as expected, but to print out the diff, Chai uses Mocha.utils.stringify(). When there are recursive objects involved, however, the whole tests fails at this point, so I've had to use this fix in my tests:

const util = require('util');
Mocha.utils.stringify = value => util.inspect(value, {depth: 5});

That prevents the test from hanging, but doesn't always work as well as Mocha's stringify function.

As an example of a test that would hang, consider:

it('should fail', () => {
  const a = {};
  const b = {a};
  a.b = b;
  assert.deepEqual(b, {});  // Expected to fail, but instead the whole test suite hangs.
});

[ScottFreeCode]

I am unable to reproduce this; I get "AssertionError: expected { a: { b: [Circular] } } to deeply equal {}"

We do still have a few issues involving circular references, though none of them appear to involve hanging that I notice:
#2598
#2559

[oleg-codaio]

Ah sorry, I never bothered testing to make sure this failed. :( It appears the issue has something to do with some more complex objects, perhaps containing getters or Proxies. Closing this for now, and will re-open if I find time to find the root cause.