### Question:
Concat extends ERE { @Override public ERE copy() { return new Concat(children.get(0).copy(), children.get(1).copy()); } private  Concat(ERE left, ERE right); static ERE get(ERE left, ERE right); @Override EREType getEREType(); @Override String toString(); @Override ERE copy(); @Override boolean containsEpsilon(); @Override ERE derive(Symbol s);  }### Answer:
@Test public void testCopy() { ERE concat = Concat.get(a, b); ERE copy = concat.copy(); assertEquals(concat, copy); }