/** Test - to check empty string are neglected */
 public void testNoEmptyStringReturnedIfCollectionOfCollectionsHasEmptyString() {
   String[][] contents = {{"a", "b", ""}, {"d"}, {"e", "f"}};
   Collection<Collection<Object>> collection = createCollections(contents);
   CodeTestExerciseCollectionOfCollectionsIterator iterator =
       new CodeTestExerciseCollectionOfCollectionsIterator(collection);
   while (iterator.hasNext()) {
     assertTrue(!iterator.next().toString().equals(""));
   }
 }
 /** Test - to check last element is returned correctly */
 public void testLastElementReturnedFromCollectionOfCollections() {
   String[][] contents = {{"a", "b", "c"}, {"d"}, {"e", "f"}};
   Collection<Collection<Object>> collection = createCollections(contents);
   CodeTestExerciseCollectionOfCollectionsIterator iterator =
       new CodeTestExerciseCollectionOfCollectionsIterator(collection);
   String lastElement = "";
   while (iterator.hasNext()) {
     lastElement = iterator.next().toString();
   }
   assertTrue(lastElement.equals("f"));
 }