public void testRemoveMergedRegion_lowlevel() {
XSSFWorkbook workbook = new XSSFWorkbook();
XSSFSheet sheet = workbook.createSheet();
CTWorksheet ctWorksheet = sheet.getCTWorksheet();
CellRangeAddress region_1 = CellRangeAddress.valueOf("A1:B2");
CellRangeAddress region_2 = CellRangeAddress.valueOf("C3:D4");
CellRangeAddress region_3 = CellRangeAddress.valueOf("E5:F6");
sheet.addMergedRegion(region_1);
sheet.addMergedRegion(region_2);
sheet.addMergedRegion(region_3);
assertEquals("C3:D4", ctWorksheet.getMergeCells().getMergeCellArray(1).getRef());
assertEquals(3, sheet.getNumMergedRegions());