### Question:
ExcelParserUtils { public static int headerIndex(String headerRef) { Objects.requireNonNull(headerRef); Matcher m = CELL_REFERENCE_REGEX.matcher(headerRef); if (m.matches()) { String alph = m.group(1); if (alph == null) { throw new IllegalArgumentException(headerRef); } else { return CellReference.convertColStringToIndex(alph); } } else { throw new IllegalArgumentException(headerRef); } } private  ExcelParserUtils(); static int headerIndex(String headerRef); static String formatAsISODateString(int numFmtId, double daysSince1Jan1900); static XMLStreamReader findFirstSheet(Iterator<InputStream> sheets); static XMLStreamReader findSheetAtIndex(Iterator<InputStream> sheets, int index); static XMLStreamReader findSheetWithName(Iterator<InputStream> sheets, String name);  }### Answer:
@Test(expected = NullPointerException.class) public void testHeaderIndexOfNullShouldThrowException() { ExcelParserUtils.headerIndex(null); }
@Test(expected = IllegalArgumentException.class) public void testHeaderIndexOfEmptyShouldThrowException() { ExcelParserUtils.headerIndex(""); }
@Test(expected = IllegalArgumentException.class) public void testHeaderIndexOfLowerCaseShouldThrowException() { ExcelParserUtils.headerIndex("ab"); }
@Test public void testHeaderIndexOfAShouldReturn0() { assertEquals(0, ExcelParserUtils.headerIndex("A")); }
@Test public void testHeaderIndexOfA1ShouldReturn0() { assertEquals(0, ExcelParserUtils.headerIndex("A1")); }
@Test public void testHeaderIndexOfA2ShouldReturn0() { assertEquals(0, ExcelParserUtils.headerIndex("A2")); }
@Test public void testHeaderIndexOfZShouldReturn25() { assertEquals(25, ExcelParserUtils.headerIndex("Z")); }
@Test public void testHeaderIndexOfAAShouldReturn26() { assertEquals(26, ExcelParserUtils.headerIndex("AA")); }
@Test public void testHeaderIndexOfAZShouldReturn51() { assertEquals(51, ExcelParserUtils.headerIndex("AZ")); }
@Test public void testHeaderIndexOfBAShouldReturn52() { assertEquals(52, ExcelParserUtils.headerIndex("BA")); }
@Test public void testHeaderIndexOfBZShouldReturn77() { assertEquals(77, ExcelParserUtils.headerIndex("BZ")); }
@Test public void testHeaderIndexOfCAShouldReturn78() { assertEquals(78, ExcelParserUtils.headerIndex("CA")); }