public static void GetKeysPreOrder_MultipleKeys_ReturnsAllKeysInCorrectOrder()
{
var tree = new BinarySearchTree <int>();
tree.AddRange(new List <int> {
5, 3, 4, 2, 7, 6, 8
});
var keys = tree.GetKeysPreOrder();
var expected = new List <int> {
5, 3, 2, 4, 7, 6, 8
};
Assert.IsTrue(keys.SequenceEqual(expected));
}