/** Some tests for the clear() method. */
 public void testClear() {
   DefaultPieDataset d = new DefaultPieDataset();
   d.addChangeListener(this);
   // no event is generated if the dataset is already empty
   d.clear();
   assertNull(this.lastEvent);
   d.setValue("A", 1.0);
   assertEquals(1, d.getItemCount());
   this.lastEvent = null;
   d.clear();
   assertNotNull(this.lastEvent);
   assertEquals(0, d.getItemCount());
 }