### Question:
MutableBinaryTreeImplKeyMapping implements KeyMapping<MutableBinaryTree> { @Override public Class<? extends MutableBinaryTree> getConcreteClass() { return MutableBinaryTreeImpl.class; }  @Override Class<? extends MutableBinaryTree> getConcreteClass(); @Override Class<MutableBinaryTree> forClass();  }### Answer:
@Test public void concreteClass() { final MutableBinaryTreeImplKeyMapping mapping = new MutableBinaryTreeImplKeyMapping(); assertEquals(MutableBinaryTreeImpl.class, mapping.getConcreteClass()); }