public void testMerge() {
Sheet sheet1 = ((BookImpl)_book).addSheet("sheet1", 256, 64*1024);
assertEquals(sheet1, _book.lookupSheet("sheet1"));
sheet1.mergeCells(0, 0, 1, 0); //A1:B1
sheet1.mergeCells(0, 1, 2, 1); //A2:C2
try {
sheet1.mergeCells(1, 0, 2, 0);
assertTrue("Shall throw ModelException for cross merging.", false);
} catch(ModelException ex) {