code: function getRealHeaderCheck(expectedHeader, caseSensitive, fieldNames) {
  
  	return function (content) {
  		let actualHeader;
  		if (caseSensitive) {
  			actualHeader = content;
  		} else {
  			actualHeader = arrayToUpperCase(content);
  			expectedHeader = arrayToUpperCase(expectedHeader);
  		}
  
  		// the header must have all the expected columns but may have more
  		return _getRealHeader(expectedHeader, actualHeader, fieldNames);
  	};
  }
docs: Creates a check which will match the future columns names to there real position
  @param expectedHeader The expected header
  @param caseSensitive Is the header case sensitive
  @param fieldNames The fieldNames to use for each field.
  @return fieldMap This maps the fieldNames to the position in the array.