Testing removeLeaf(). Removing one node from 6-node tree.
Removing another node from 5-node tree.
Attempting to remove non-leaf node from 4-node tree.
Operation should have no effect.
Attempting to remove invalid node from 4-node tree.
The tree looks like this:
[The above sequence should be 1, 12, 13, 131.]
Removing remaining nodes from 4-node tree.