Help with assignment

Question

I have already done part 1 but I cant get part 2 can someone please help me and give me a good example or show me the correct way to do #2
my part one looks like this :
import java.text.DecimalFormat;
public class ElapsedTime {
     private int nDays;
     private int nHours;
     private int nMinutes;
     private int ETime;
     //This creats an object of ElapsedTime in total minutes
     public ElapsedTime(int days, int hours, int minutes) {
          nDays = days * 1440;
          nHours= hours *60;
          nMinutes= minutes;
          ETime = nDays + nHours + nMinutes;
          ETime = Math.abs(ETime);
     //This sets the current time interval according to its parameters
     public void setTime(int days, int hours, int minutes){
          ETime = (days * 1440) + (hours * 60) + minutes;
          ETime = Math.abs(ETime);
     //This adds time to the current time interval
     public void addTime(int days, int hours, int minutes){
          ETime += (days * 1440) + (hours * 60) + minutes;
          ETime = Math.abs(ETime);
     //This returns the number of days in the current time interval
     public int getDays(){
          nDays = ETime / 1440;
          return (nDays);
     //This returns the number of hours in the current time interval
     public int getHours(){
          nHours = (ETime % 1440) / 60;
          return (nHours);
     //calculates and stores the number of minutes with the remainder minutes
     //of the getHours() method
     public int getMinutes(){
          nMinutes = (ETime % 1440) % 60;
          return (nMinutes);
     //This returns a String object representing the current time interval
     //in days, hours and minutes
     public String toString(){
          DecimalFormat fmt = new DecimalFormat("00");
          return (getDays() + ":" + fmt.format(getHours()) + ":" + fmt.format(getMinutes()));
Part 1. Write a class to represent a time interval, named ElapsedTime. This class represents elapsed time in days, hours, and minutes. It might be used by a shipping company to estimate and keep track of how long their vessels are at sea. If the trip takes 7 1/2 days, the elapsed time would be 7 days, 12 hours and 0 minutes. Represent the current time interval as a number of minutes, stored in an int Java variable.
Constructor: ElapsedTime(int days, int hours, int minutes)
This creates an object of the ElapsedTime class whose instance data is initialized according to the parameters of the constructor. For example, if the invocation of the constructor is ElapsedTime(0, 0, 0) an object is created representing a time interval of zero minutes. You may assume that all three parameters are never negative.
Other public methods:
void setTime(int days, int hours, int minutes)
setTime sets the current time interval according to its parameters. For example, if the method invocation is setTime(7,3,22) the time interval is 10,282 minutes. If the method invocation is setTime(0,0,10282) the time interval is set the same as in the previous example. You may assume that all three parameters are never negative.
void addTime(int days, int hours, int minutes)
addTime adds to the object's current time interval according to its parameters. For example, if the method invocation is addTime(1,0,0) the time interval is increased by 1440 minutes (there are 1440 minutes in a day). One or all of the three parameters may be negative or zero. Use the class method Math.abs() to make sure that your instance data (the number of minutes) is always non-negative. For example, if the current time interval is 1 minute, and the method invocation is addTime(0,0,-2) the resultant time interval should be 1 minute (NOT -1 minute).
int getDays()
getDays returns the number of days not exceeded by the current time interval. This is never negative. For example, if the current time interval is 1439 minutes (one minute short of a day), getDays will return 0. If the current time interval is 1441 minutes (one minute more than a day), getDays will return 1.
int getHours()
getHours returns the number of hours in the current time interval after all whole days are taken out. This is never negative and never exceeds 23. For example, if the current time interval is 1439 minutes (one minute short of a day), getHours will return 23. If the current time interval is 1441 minutes (one minute more than a day), getHours will return 0.
int getMinutes()
getMinutes returns the number of minutes in the current time interval after all whole days and all whole hours are taken out. This is never negative and never exceeds 59. For example, if the current time interval is 1439 minutes (one minute short of a day), getMinutes will return 59. If the current time interval is 1441 minutes (one minute more than a day), getMinutes will return 1.
String toString()
toString returns a String object representing the current time interval in days, hours and minutes. The form of the String should be <days>:<hours>:<minutes>, where <days> is at least one digit, <hours> is always two digits between 00 and 23 and <minutes> is always two digits between 00 and 59. You can use the DecimalFormat class with a pattern of "00" to force a number to be represented by a string with a leading zero. For example, if the current time interval is 1441 minutes (one minute more than a day), the String object will contain 1:00:01. If the current time interval is 1439 minutes (one minute less than a day) the String object will contain 0:23:59.
Part 2. Write a test program to test the ElapsedTime class. The program should be written as a separate class. In the test program, test each method with parameters supplied by your program to see if it works. Test programs like this are usually rather long (several pages) but pretty simple to write. For each test, use JOptionPane.showMessageDialog() (or System.out.println) to output what the test is and what the results are. For example, suppose you are testing the constructor and the toString method. You call the constructor as ElapsedTime(0,0,1441). The JOptionPane would look like:

Answer 1

Well, in this instance, I am for once happy with what a teacher is teaching. Test driven development is a good thing, and I am glad to see students are learning it early. (We would do well to do the same where I am working!)
That having been said, you have two options: either System.out.println() or using a Swing dialog. IMO, the former is a lot easier. You will have to write boilerplate Swing code just to get the dialog to show. So, if the assignment is agnostic as to which method you should use to validate your test results, go for println().
As for writing the test class itself, this is normally an easy process. Create another class and give it a main() method. You can execute all your tests within the main() method itself, so a constructor, methods, etc. will not be necessary.
What you want to do is create an instance of your test object. This will in effect test your constructor. If there are multiple constructors, instantiate your object with each possible constructor. Then move onto the methods. If a given constructor sets instance variables, you can complete several test steps in one execution by calling the relevant accessor (getter) methods in the target class. Call mutator (setter) methods and then call the accessor methods to validate the variables are being set and retrieved properly. Finally, call any algorithm or calculation intensive methods.
Generally, you will want to use the same set of test data for each run. So, you should be able to pre-calculate the results of any algorithms ahead of time. Verify in your testing class that the result of the method is as expected.
- Saish