* (related to MNG-6572 optimization)
     */
    @Test
    void testVersionEqualWithLeadingZeroes() {
        // versions with string lengths from 1 to 19
        String[] arr = new String[] {
            "0000000000000000001",
            "000000000000000001",
            "00000000000000001",
            "0000000000000001",
            "000000000000001",

                    unfiltered.add("yyy");
                    unfiltered.addAll(ImmutableList.copyOf(elements));
                    unfiltered.add("zzz");
                    return Sets.filter(unfiltered, Collections2Test.LENGTH_1);
                  }
                })
            .named("Sets.filter, no nulls")
            .withFeatures(
                CollectionFeature.SUPPORTS_ADD,
                CollectionFeature.SUPPORTS_REMOVE,

    assertFalse(elementsEqual(b.iterator(), a.iterator()));

    // Different lengths.
    a = asList(4, 8, 15, 16, 23);
    b = asList(4, 8, 15, 16, 23, 42);
    assertFalse(elementsEqual(a.iterator(), b.iterator()));
    assertFalse(elementsEqual(b.iterator(), a.iterator()));

    // Different lengths, one is empty.
    a = emptySet();
    b = asList(4, 8, 15, 16, 23, 42);

    assertFalse(elementsEqual(b.iterator(), a.iterator()));

    // Different lengths.
    a = asList(4, 8, 15, 16, 23);
    b = asList(4, 8, 15, 16, 23, 42);
    assertFalse(elementsEqual(a.iterator(), b.iterator()));
    assertFalse(elementsEqual(b.iterator(), a.iterator()));

    // Different lengths, one is empty.
    a = emptySet();
    b = asList(4, 8, 15, 16, 23, 42);

    a = Arrays.<@Nullable Integer>asList(4, 8, 15, null, 23, 42);
    b = asList(4, 8, 15, 16, 23, 42);
    assertFalse(elementsEqual(a, b));
    assertFalse(elementsEqual(b, a));

    // Different lengths.
    a = asList(4, 8, 15, 16, 23);
    b = asList(4, 8, 15, 16, 23, 42);
    assertFalse(elementsEqual(a, b));
    assertFalse(elementsEqual(b, a));
  }

  public void testToString() {