Untested? I've read that there were 137 total faithless electors since the founding. It's happened before, just never enough to swing an election.
Untested in court, specifically regarding laws against being faithless electors. But untested in general.
23 of them refused to vote for Van Buren's VP because he was sleeping with a black woman and admitted it. Another 32 were also related to Van Buren, don't recall the why specifically. 63 were because Horace Greeley died before taking office. That's the virtual majority. The rest were ones or twos.