fn test_split_off_empty_right() {
    let mut data = rand_data(173);

    let mut set = BTreeSet::from_iter(data.clone());
    let right = set.split_off(&(data.iter().max().unwrap() + 1));

    data.sort();
    assert!(set.into_iter().eq(data));
    assert!(right.into_iter().eq(None));
}
A view into a vacant entry in a `BTreeMap`.
It is part of the [`Entry`] enum.
benchmarks/haystacks/code/rust-library.rs