deepEqual should not infinitely recurse an infinite lazy getter chain

Tell us about your runtime:

• QUnit version: 2.7.1
• What environment are you running QUnit in? (e.g., browser, Node): Browser
• How are you running QUnit? (e.g., script, testem, Grunt): Script

What are you trying to do?

Code that reproduces the problem:

https://jsfiddle.net/bzomqak8/11/

class Foo {
  constructor(a = 1) {
    this.a = a;
  }
}

Object.defineProperty(Foo.prototype, 'b', {
  enumerable: true,
  get() {
    return new Foo(this.a + 1);
  }
})

QUnit.test("hello test", function(assert) {
  assert.deepEqual(new Foo(), new Foo());
});

If you have any relevant configuration information, please include that here:

What did you expect to happen?

I expected QUnit to not compare computed properties.

What actually happened?

QUnit compares computed properties by using a for..in loop which (due to BFS) recurses infinitely without ever hitting a stack limit.

This is a minimal reproduction extracted from one of our Ember apps. In the actual app we use an Ember.Object and a computed property instead of the code above, but the effect is the same.

Start at QUnit's deepEqual entry point and reproduce the case from the linked jsfiddle using the Foo getter chain shown in the issue. Done means the comparison terminates instead of recursing indefinitely and handles the computed property according to the reported expectation.