DataFormatter formatter = new HSSFDataFormatter(Locale.ENGLISH); // Ok Assert.assertEquals("12334567890123", formatter.formatRawCellContents(12334567890123.0, 0, "0")); // Ok Assert.assertEquals("12334567890123", formatter.formatRawCellContents(12334567890123.0, 0, "#")); // Ok Assert.assertEquals("12334567890123", formatter.formatRawCellContents(12334567890123.0, 0, "#0")); // Fails expected:<1[233456789012]3> but was:<1[.23346E1]3> Assert.assertEquals("12334567890123", formatter.formatRawCellContents(12334567890123.0, 0, "0#"));