### Question:
EmptyConstructor implements EmptyTreeConstructor<E, MutableBinaryTreeNode<E>, MutableBinaryTreeImpl<E>> { @Override public MutableBinaryTreeImpl<E> build() { return new MutableBinaryTreeImpl<>(); }  @Override MutableBinaryTreeImpl<E> build(); @Override Class<? extends Tree> forClass();  }### Answer:
@Test public void build() { final EmptyConstructor<String> constructor = new EmptyConstructor<>(); assertTrue(constructor.build() instanceof MutableBinaryTreeImpl); }