isIterable() has a case of false positives.

[segayuu]

iterable must have an [@@iterator]() method and its return value must be an iterator.
iterator must have an next() method and its return value must be an iteratorResult.
iteratorResult is an object, it must have a boolean done property, and when done property is false, value property must be present.

In other words, if chai really say iterable, it should be possible to get iteratorResult!

It is difficult to obtain iteratorResult on the premise that there are no side effects. (Ex: queue, stack)
However, when calling [@@iterator]() it is very uncommon case that there are side effects other than for debugging purposes.

if (!(value != null && typeof value[Symbol.iterator] === 'function')) {
  return false;
}
const maybeIterator = value[Symbol.iterator]();
if (typeof maybeIterator !== 'object' || typeof maybeIterator.next !== 'function') {
  return false;
}
return true;