### Question:
CNode extends MainNode<K, V> { static VerifyException invalidElement(final BasicNode elem) { throw new VerifyException("A CNode can contain only CNodes and SNodes, not " + elem); } private  CNode(final Gen gen, final int bitmap, final BasicNode... array);   CNode(final Gen gen); @Override String toString();  }### Answer:
@Test public void testInvalidElement() { assertThrows(VerifyException.class, () -> CNode.invalidElement(null)); }