public void UpdateOrAdd2()
{
ICollection <String> coll = new HashBag <String>();
// s1 and s2 are distinct objects but contain the same text:
String s1 = "abc", s2 = ("def" + s1).Substring(3);
Assert.IsFalse(coll.UpdateOrAdd(s1, out string old));
Assert.AreEqual(null, old);
Assert.IsTrue(coll.UpdateOrAdd(s2, out old));
Assert.IsTrue(Object.ReferenceEquals(s1, old));
Assert.IsFalse(Object.ReferenceEquals(s2, old));
}
