### Question:
Epsilon extends ERE { @Override public ERE derive(Symbol s) { return Empty.get(); } private  Epsilon(); static Epsilon get(); @Override EREType getEREType(); @Override boolean equals(Object o); @Override int compareTo(Object o); @Override ERE copy(); @Override String toString(); @Override boolean containsEpsilon(); @Override ERE derive(Symbol s);  }### Answer:
@Test public void testDerive() { ERE derived = epsilon.derive(Symbol.get("test")); Empty empty = Empty.get(); assertEquals(empty, derived); }