### Question:
TransactionList extends TransformedList<E, E> { public void beginEvent() { beginEvent(true); } 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 testDoubleBegin() { txList.beginEvent(); try { txList.beginEvent(); } catch (IllegalStateException e) { assertEquals("Unable to begin a new transaction before committing or rolling back the previous transaction", e.getMessage()); } }