* set would be sufficient to expose any possible bug. Brute force is simpler.
 *
 * <p>To use this class the concrete subclass must implement the {@link
 * IteratorTester#newTargetIterator()} method. This is because it's impossible to test an Iterator
 * without changing its state, so the tester needs a steady supply of fresh Iterators.
 *

          protected Iterator<Integer> newTargetIterator() {
            return ImmutableList.of(1, 2).iterator();
          }
        };
    assertFailure(tester);
  }

  public void testUnknownOrder() {
    new IteratorTester<Integer>(
        3, MODIFIABLE, newArrayList(1, 2), IteratorTester.KnownOrder.UNKNOWN_ORDER) {
      @Override
      protected Iterator<Integer> newTargetIterator() {

        4,
        MODIFIABLE,
        getSubjectGenerator().order(asList(e0(), e1(), e1(), e2())),
        IteratorTester.KnownOrder.KNOWN_ORDER) {
      @Override
      protected Iterator<E> newTargetIterator() {
        return getSubjectGenerator().create(e0(), e1(), e1(), e2()).iterator();
      }
    }.test();
  }

  @CollectionFeature.Require(value = SUPPORTS_ITERATOR_REMOVE, absent = KNOWN_ORDER)

        4,
        MODIFIABLE,
        getSubjectGenerator().order(asList(e0(), e1(), e1(), e2())),
        IteratorTester.KnownOrder.KNOWN_ORDER) {
      @Override
      protected Iterator<E> newTargetIterator() {
        return getSubjectGenerator().create(e0(), e1(), e1(), e2()).iterator();
      }
    }.test();
  }

  @CollectionFeature.Require(value = SUPPORTS_ITERATOR_REMOVE, absent = KNOWN_ORDER)

          protected Iterator<Integer> newTargetIterator() {
            return ImmutableList.of(1, 2).iterator();
          }
        };
    assertFailure(tester);
  }

  public void testUnknownOrder() {
    new IteratorTester<Integer>(
        3, MODIFIABLE, newArrayList(1, 2), IteratorTester.KnownOrder.UNKNOWN_ORDER) {
      @Override
      protected Iterator<Integer> newTargetIterator() {

      @Override
      protected Iterator<Integer> newTargetIterator() {
        return Iterators.cycle(asList(1, 2));
      }
    }.test();
  }

  @GwtIncompatible // slow (~5s)
  public void testConcatNoIteratorsYieldsEmpty() {
    new EmptyIteratorTester() {
      @Override
      protected Iterator<Integer> newTargetIterator() {
        return Iterators.concat();
      }
    }.test();
  }

      @Override
      protected Iterator<Integer> newTargetIterator() {
        return Iterators.cycle(asList(1, 2));
      }
    }.test();
  }

  @GwtIncompatible // slow (~5s)
  public void testConcatNoIteratorsYieldsEmpty() {
    new EmptyIteratorTester() {
      @Override
      protected Iterator<Integer> newTargetIterator() {
        return Iterators.concat();
      }
    }.test();
  }

        newLinkedHashSet(asList(2, 3, 4, 7, 8)),
        IteratorTester.KnownOrder.KNOWN_ORDER) {
      private @Nullable Multimap<String, Integer> multimap;

      @Override
      protected Iterator<Integer> newTargetIterator() {
        multimap = LinkedHashMultimap.create();
        multimap.putAll("foo", asList(2, 3, 4));
        multimap.putAll("bar", asList(5, 6));
        multimap.putAll("foo", asList(7, 8));

      super(master.size() + 3, MODIFIABLE, master, IteratorTester.KnownOrder.KNOWN_ORDER);
      this.master = master;
    }

    @Override
    protected Iterator<T> newTargetIterator() {
      // make copy from master to verify later
      targetList = Lists.newArrayList(master);
      Iterator<T> iterator = targetList.iterator();
      return Iterators.peekingIterator(iterator);
    }

        private @Nullable LinkedListMultimap<String, Integer> multimap;

        @Override
        protected ListIterator<Entry<String, Integer>> newTargetIterator() {
          multimap = create();
          multimap.putAll("foo", asList(2, 3));
          multimap.putAll("bar", asList(4, 5));
          multimap.put("foo", 6);