public void TestCacheWorks()
{
var init = new int[] { 2, 3, 4, 5 };
var t = new RedBlackSetTester<int>(init);
Assert.That(t.Cache, Is.EqualTo(init));
Assert.That(t.Remove(4), Is.True);
var remove = init.Where(i => i != 4);
Assert.That(t.Add(2), Is.False);
Assert.That(t.Cache, Is.EquivalentTo(remove));
Assert.That(t.Add(7), Is.True);
var add = remove.Concat(Enumerable.Repeat(7, 1));
Assert.That(t.Cache, Is.EquivalentTo(add));
t.Clear();
Assert.That(t.Cache, Is.Empty);
}