Here is a JUnit method Anna used to test removing the root. It kept reporting failure, but Anna could see nothing wrong with remove()’s implementation. After a frustrating hour of trying to solve the problem, Anna was floored when Opal walked by and pointed immediately to the mistake. What did Opal see?

Question

```
public void testRemoveRoot(){
BinaryTreeNode root = tree3.root();
integer target = root.element();
// remove target from tree3 and the list of elements
// we expect to see in tree3
expectedTree3List.remove( target );
tree3.remove( root );
assertTrue( !tree3.contains( target ) );
ToListVisitor treeVisitor = new ToListVisitor();
tree3.preOrderTraversal( treeVisitor );
assertTrue( expectedTree3List.equals( treeVisitor.list() ) );
}

```

Answer 1

The remove() method will pull a leaf node up to replace the value formerly in the root. Thus expectedTree3List and tre3Visitor.list() will have the same elements, but not necessarily in the same order. Consequently the last assertTrue() will report false.