Thanks a lot Prankster! I really appreciate it..here is the
fileMultiHashMapTest.java



import java.util.*;

public class MultiHashMapTest {

    /** Objects to be used as keys */

    private static final Object o1 = new Object();

    private static final Object o2 = new Object();

    private static final Object o3 = new Object();

    private static final Object o4 = new Object();

    /** Strings to be used as values */

    private static final String s1 = "one";

    private static final String s2 = "two";

    private static final String s3 = "three";

    private static final String s4 = "four";

    /** Collections to be used to test */

    private static final Collection c12 = new Vector();

    private static final Collection c12n = new Vector();

    /** Main entry point to program */

    public static void main(String[] args) {

     setupCollections();

     try {

         testMHM();

     } catch (Exception excn) {

         excn.printStackTrace();

     }

    }

    public static void setupCollections() {

     c12.add(s1);

     c12.add(s2);

     c12n.addAll(c12);

     c12n.add(null);

    }

    public static void testMHM() throws CheckFailedException {

     MultiHashMap mhm = new MultiHashMap();

     check("Assigning value to a key that was not in before", mhm.put(o1, s1) == null);

     check("Verifying association caused by put", s1.equals(mhm.get(o1)));

     check("Verifying return value when reassigning a key to a value", s1.equals(mhm.put(o1, s2)));

     checkEqualCollection("Verifying getAll method", c12, mhm.getAll(o1));

     mhm.putAll(o3, c12);

     checkEqualCollection("Verifying putAll method", c12, mhm.getAll(o3));

     mhm.put(o3, null);

     checkEqualCollection("Verifying the ability to add null values with put method", c12n, mhm.getAll(o3));

     check("Verifying the contains method works for null", mhm.contains(o3, null));

     check("Verifying the contains method works", mhm.contains(o3, s1));

     check("Verifying remove method return value", mhm.remove(o3, null));

     check("Verifying remove method works", !mhm.contains(o3, null));

     checkEqualCollection("Verifying HashMap remove method return value", (Collection) mhm.remove(o3), c12);

     check("Verifying HashMap remove method works", mhm.get(o3) == null);

    }

   

    public static void check(String message, boolean result) throws CheckFailedException {

     if (result == false)

         throw new CheckFailedException(message + " failed");

     else

         System.out.println(message + " passed");

    }

    public static void checkEqualCollection(String message, Collection c1, Collection c2) throws CheckFailedException {

     check(message, c1.containsAll(c2) && c2.containsAll(c1));

    }

    private static class CheckFailedException extends Exception {

     public CheckFailedException() { super(); }

     public CheckFailedException(String message) { super(message); }

    }

}