### Question:
TransactionList extends TransformedList<E, E> { public void rollbackEvent() { if (rollbackSupport == null) throw new IllegalStateException("This TransactionList does not support rollback"); if (txContextStack.isEmpty()) throw new IllegalStateException("No ListEvent exists to roll back"); txContextStack.remove(txContextStack.size()-1).rollback(); } TransactionList(EventList<E> source);   TransactionList(EventList<E> source, boolean rollbackSupport); void beginEvent(); void beginEvent(boolean buffered); void commitEvent(); void rollbackEvent(); @Override void dispose(); @Override void listChanged(ListEvent<E> listChanges);  }### Answer:
@Test public void testRollbackNothing() { try { txList.rollbackEvent(); } catch (IllegalStateException e) { assertEquals("No ListEvent exists to roll back", e.getMessage()); } }