### Question:
Negation extends ERE { @Override public ERE derive(Symbol s) { return Negation.get(children.get(0).derive(s)); } private  Negation(ERE child); static ERE get(ERE child); @Override EREType getEREType(); @Override String toString(); @Override ERE copy(); @Override boolean containsEpsilon(); @Override ERE derive(Symbol s);  }### Answer:
@Test public void testDerive() { ERE negateEmpty = Negation.get(empty); ERE negateEpsilon = Negation.get(epsilon); ERE derived = negateEpsilon.derive(Symbol.get("test")); assertEquals(negateEmpty, derived); }