@Test
 public void testDateFormat() throws Exception {
   TimeZone tz = LocaleUtil.getUserTimeZone();
   LocaleUtil.setUserTimeZone(TimeZone.getTimeZone("CET"));
   try {
     runFormatTests(
         "DateFormatTests.xlsx",
         new CellValue() {
           public Object getValue(Cell cell) {
             return cell.getDateCellValue();
           }
         });
   } finally {
     LocaleUtil.setUserTimeZone(tz);
   }
 }
 /**
  * Creates a format tracking wrapper around the given listener, using the {@link
  * Locale#getDefault() default locale} for the formats.
  */
 public FormatTrackingHSSFListener(HSSFListener childListener) {
   this(childListener, LocaleUtil.getUserLocale());
 }
 @AfterClass
 public static void resetLocale() {
   LocaleUtil.setUserLocale(userLocale);
 }
 @BeforeClass
 public static void initLocale() {
   userLocale = LocaleUtil.getUserLocale();
   LocaleUtil.setUserLocale(Locale.ROOT);
 }
  @Test
  public void dateCells() throws Exception {
    Workbook workbook = _testDataProvider.createWorkbook();
    fixFonts(workbook);
    Sheet sheet = workbook.createSheet();
    DataFormat df = workbook.getCreationHelper().createDataFormat();

    CellStyle style1 = workbook.createCellStyle();
    style1.setDataFormat(df.getFormat("m"));

    CellStyle style3 = workbook.createCellStyle();
    style3.setDataFormat(df.getFormat("mmm"));

    CellStyle style5 = workbook.createCellStyle(); // rotated text
    style5.setDataFormat(df.getFormat("mmm/dd/yyyy"));

    Calendar calendar = LocaleUtil.getLocaleCalendar(2010, 0, 1); // Jan 1 2010

    Row row = sheet.createRow(0);
    row.createCell(0).setCellValue(DateUtil.getJavaDate(0)); // default date

    Cell cell1 = row.createCell(1);
    cell1.setCellValue(calendar);
    cell1.setCellStyle(style1);
    row.createCell(2).setCellValue("1"); // column 1 should be sized as '1'

    Cell cell3 = row.createCell(3);
    cell3.setCellValue(calendar);
    cell3.setCellStyle(style3);
    row.createCell(4).setCellValue("Jan");

    Cell cell5 = row.createCell(5);
    cell5.setCellValue(calendar);
    cell5.setCellStyle(style5);
    row.createCell(6).setCellValue("Jan/01/2010");

    Cell cell7 = row.createCell(7);
    cell7.setCellFormula("DATE(2010,1,1)");
    cell7.setCellStyle(style3); // should be sized as 'Jan'

    // autosize not-evaluated cells, formula cells are sized as if the result is 0
    for (int i = 0; i < 8; i++) sheet.autoSizeColumn(i);

    assertEquals(sheet.getColumnWidth(2), sheet.getColumnWidth(1)); // date formatted as 'm'
    assertTrue(sheet.getColumnWidth(3) > sheet.getColumnWidth(1)); // 'mmm' is wider than 'm'
    assertEquals(sheet.getColumnWidth(4), sheet.getColumnWidth(3)); // date formatted as 'mmm'
    assertTrue(
        sheet.getColumnWidth(5) > sheet.getColumnWidth(3)); // 'mmm/dd/yyyy' is wider than 'mmm'
    assertEquals(
        sheet.getColumnWidth(6), sheet.getColumnWidth(5)); // date formatted as 'mmm/dd/yyyy'

    // YK: width of not-evaluated formulas that return data is not determined
    // POI seems to conevert '0' to Excel date which is the beginng of the Excel's date system

    // evaluate formulas and re-autosize
    evaluateWorkbook(workbook);

    for (int i = 0; i < 8; i++) sheet.autoSizeColumn(i);

    assertEquals(sheet.getColumnWidth(2), sheet.getColumnWidth(1)); // date formatted as 'm'
    assertTrue(sheet.getColumnWidth(3) > sheet.getColumnWidth(1)); // 'mmm' is wider than 'm'
    assertEquals(sheet.getColumnWidth(4), sheet.getColumnWidth(3)); // date formatted as 'mmm'
    assertTrue(
        sheet.getColumnWidth(5) > sheet.getColumnWidth(3)); // 'mmm/dd/yyyy' is wider than 'mmm'
    assertEquals(
        sheet.getColumnWidth(6), sheet.getColumnWidth(5)); // date formatted as 'mmm/dd/yyyy'
    assertEquals(
        sheet.getColumnWidth(4), sheet.getColumnWidth(7)); // date formula formatted as 'mmm'

    workbook.close();
  }