public void TryAdd_should_return_false_when_trying_to_overwrite_existing_elements() { for (int i = 0; i < 1000; i++) { var key = Guid.NewGuid(); dic.Add(key, "value"); dic.TryAdd(key, "value2").Should().BeFalse(); dic.TryAdd(key, "value2").Should().BeFalse(); } }