Yes, pretty sure they have been. There is a sizable mountain of evidence to support that they have, and still are. There are quite a few -very- important cases, that no one has gotten close to explaining away. When craft are so advanced that they can only belong to a superpower nation or are not from around these parts, makes it easier to break down.
And I for a moment, don't believe that they have tested black projects over major cities, for extended periods.