s1.add(2.0, 2.2);
s1.add(3.0, 3.3);
assertEquals(3, s1.getItemCount());
s1.clear();
assertEquals(0, s1.getItemCount());
assertTrue(Double.isNaN(s1.getMinX()));
assertTrue(Double.isNaN(s1.getMaxX()));
assertTrue(Double.isNaN(s1.getMinY()));
assertTrue(Double.isNaN(s1.getMaxY()));