Calculate Datetime difference with output in this format "xx year(s) xx month(s) xx day(s)"

DatetimeDiffWithFormat

import org.joda.time.DateTime;
import org.joda.time.DateTimeZone;
import org.joda.time.Duration;
import org.joda.time.Period;

class DatetimeDiffWithFormat{
  /**
   * @param DateTime start
   * @param DateTime end
   * @param UnitDMYENUM unit
   * @return String result with format like "xx year(s) xx month(s) xx day(s)"
   */
public String minusDate(DateTime start,DateTime end, UnitDMYENUM unit){
		if (start==null || end ==null) return "";
		
		String years = " year(s) ";
		String months = " month(s) ";
		String days = " day(s)";
		
		StringBuffer result = new StringBuffer("");
		
		if(start.isAfter(end)){
			return result.toString();
		}
		
		if(unit==null){
			Period btw = Period.fieldDifference(start.toLocalDate(), end.toLocalDate().plusDays(1));
			int y = btw.getYears();
			int m = btw.getMonths();
			int d = btw.getDays();
			if(y!=0){
				result.append(y);
				result.append(years);
			}
			if(m!=0){
				result.append(m);
				result.append(months);
			}
			if(d!=0){
				result.append(d);
				result.append(days);
			}
		}else if(unit == UnitDMY.DAY){
			Duration duration = new Duration(start, end.plusDays(1));
			result.append((int)duration.getStandardDays());
			result.append(days);
		}else if(unit == UnitDMY.MONTH){
			Period btw = Period.fieldDifference(start.toLocalDate(), end.toLocalDate().plusDays(1));
			int y = btw.getYears();
			int m = btw.getMonths();
			if(y>=1){
				m += y*12;
			}
			if(m!=0){
				result.append(m);
				result.append(months);
			}
		}else if(unit == UnitDMY.YEAR){
			Period btw = Period.fieldDifference(start.toLocalDate(), end.toLocalDate().plusDays(1));
			int y = btw.getYears();
			if(y!=0){
				result.append(y);
				result.append(years);
			}
		}
		return result.toString().trim();
	}	
	
	public enum UnitDMY{
		DAY,
		MONTH,
		YEAR;
	}
}

TestCases

  @Test
	public void testMinusDateDateTimeDateTimeUnitDMY() {
		DateTime start1 = new DateTime(2013,2,1,0,0);
		DateTime end1 = new DateTime(2013,2,1,0,0);
		assertEquals("1 day(s)",DateTimeFormatTool.minusDate(start1, end1, UnitDMY.DAY));
		System.out.println("Start: "+start1);
		System.out.println("End: "+end1);
		System.out.println("result: "+DateTimeFormatTool.minusDate(start1, end1, UnitDMY.DAY));
		
		DateTime start2 = new DateTime(2012,2,1,0,0);
		DateTime end2 = new DateTime(2013,2,28,0,0);
		assertEquals("394 day(s)",DateTimeFormatTool.minusDate(start2, end2, UnitDMY.DAY));
		System.out.println("Start: "+start2);
		System.out.println("End: "+end2);
		System.out.println("result: "+DateTimeFormatTool.minusDate(start2, end2));
		
		DateTime start3 = new DateTime(2012,2,1,0,0);
		DateTime end3 = new DateTime(2012,2,10,0,0);
		assertEquals("10 day(s)",DateTimeFormatTool.minusDate(start3, end3, null));
		
		DateTime start4 = new DateTime(2013,2,1,0,0);
		DateTime end4 = new DateTime(2013,2,28,0,0);
		assertEquals("1 month(s)",DateTimeFormatTool.minusDate(start4, end4, null));
		
		DateTime start5 = new DateTime(2012,2,1,0,0);
		DateTime end5 = new DateTime(2012,2,29,0,0);
		assertEquals("1 month(s)",DateTimeFormatTool.minusDate(start5, end5, null));
		
		DateTime start6 = new DateTime(2012,3,1,0,0);
		DateTime end6 = new DateTime(2012,4,29,0,0);
		assertEquals("1 month(s) 29 day(s)",DateTimeFormatTool.minusDate(start6, end6, null));
		
		DateTime start7 = new DateTime(2012,3,1,0,0);
		DateTime end7 = new DateTime(2012,3,30,0,0);
		assertEquals("30 day(s)",DateTimeFormatTool.minusDate(start7, end7, null));
		
		DateTime start8 = new DateTime(2012,3,1,0,0);
		DateTime end8 = new DateTime(2014,3,30,0,0);
		assertEquals("2 year(s) 30 day(s)",DateTimeFormatTool.minusDate(start8, end8, null));
		
		DateTime start9 = new DateTime(2012,3,1,0,0);
		DateTime end9 = new DateTime(2014,4,3,0,0);
		assertEquals("2 year(s) 1 month(s) 3 day(s)",DateTimeFormatTool.minusDate(start9, end9, null));
		
		DateTime start10 = new DateTime(2012,3,1,0,0);
		DateTime end10 = new DateTime(2014,4,3,0,0);
		assertEquals("25 month(s)",DateTimeFormatTool.minusDate(start10, end10, UnitDMY.MONTH));
		
		DateTime start11 = new DateTime(2012,3,1,0,0);
		DateTime end11 = new DateTime(2012,3,3,0,0);
		assertEquals("",DateTimeFormatTool.minusDate(start11, end11, UnitDMY.MONTH));
		
		DateTime start12 = new DateTime(2012,3,1,0,0);
		DateTime end12 = new DateTime(2012,3,3,0,0);
		assertEquals("",DateTimeFormatTool.minusDate(start12, end12, UnitDMY.YEAR));
		
		DateTime start13 = new DateTime(2012,3,1,0,0);
		DateTime end13 = new DateTime(2013,3,3,0,0);
		assertEquals("1 year(s)",DateTimeFormatTool.minusDate(start13, end13, UnitDMY.YEAR));
		
		DateTime start14 = new DateTime(2012,3,1,0,0);
		DateTime end14 = new DateTime(2012,9,3,0,0);
		assertEquals("",DateTimeFormatTool.minusDate(start14, end14, UnitDMY.YEAR));
	}