* called more than once to add features in multiple groups.
   */
  @CanIgnoreReturnValue
  public B withFeatures(Feature<?>... features) {
    return withFeatures(asList(features));
  }

  @CanIgnoreReturnValue
  public B withFeatures(Iterable<? extends Feature<?>> features) {
    for (Feature<?> feature : features) {
      this.features.add(feature);
    }
    return self();

                    return Sets.union(Sets.<String>newHashSet(), Sets.<String>newHashSet());
                  }
                })
            .named("empty U empty")
            .withFeatures(
                CollectionSize.ZERO, CollectionFeature.NONE, CollectionFeature.ALLOWS_NULL_VALUES)
            .createTestSuite());

    suite.addTest(
        SetTestSuiteBuilder.using(

              @Override
              public Set<String> create(String[] elements) {
                return emptySet();
              }
            })
        .named("emptySet")
        .withFeatures(CollectionFeature.SERIALIZABLE, CollectionSize.ZERO)
        .suppressing(suppressForEmptySet())
        .createTestSuite();
  }

  public Test testsForSingletonSet() {
    return SetTestSuiteBuilder.using(

                    }
                    return multimap;
                  }
                })
            .named("synchronized ArrayListMultimap")
            .withFeatures(
                MapFeature.ALLOWS_NULL_KEYS,
                MapFeature.ALLOWS_NULL_VALUES,
                MapFeature.ALLOWS_ANY_NULL_QUERIES,
                MapFeature.GENERAL_PURPOSE,

                    return table.rowKeySet();
                  }
                })
            .named("HashBasedTable.rowKeySet")
            .withFeatures(COLLECTION_FEATURES_REMOVE)
            .withFeatures(CollectionFeature.SUPPORTS_ITERATOR_REMOVE)
            .createTestSuite());

    suite.addTest(
        SortedSetTestSuiteBuilder.using(

                    return table.rowKeySet();
                  }
                })
            .named("HashBasedTable.rowKeySet")
            .withFeatures(COLLECTION_FEATURES_REMOVE)
            .withFeatures(CollectionFeature.SUPPORTS_ITERATOR_REMOVE)
            .createTestSuite());

    suite.addTest(
        SortedSetTestSuiteBuilder.using(

                return Collections.checkedNavigableSet(innerSet, String.class);
              }
            })
        .named("checkedNavigableSet/TreeSet, natural")
        .withFeatures(
            SetFeature.GENERAL_PURPOSE,
            CollectionFeature.KNOWN_ORDER,
            CollectionFeature.SERIALIZABLE,
            CollectionFeature.FAILS_FAST_ON_CONCURRENT_MODIFICATION,

            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.KNOWN_ORDER,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .named("Multisets.unmodifiableMultiset[TreeMultiset]")
            .createTestSuite());

    suite.addTest(
        MultisetTestSuiteBuilder.using(unionGenerator())

              @Override
              public List<String> create(String[] elements) {
                return emptyList();
              }
            })
        .named("emptyList")
        .withFeatures(CollectionFeature.SERIALIZABLE, CollectionSize.ZERO)
        .suppressing(suppressForEmptyList())
        .createTestSuite();
  }

  public Test testsForSingletonList() {
    return ListTestSuiteBuilder.using(

              @Override
              public List<String> create(String[] elements) {
                return emptyList();
              }
            })
        .named("emptyList")
        .withFeatures(CollectionFeature.SERIALIZABLE, CollectionSize.ZERO)
        .suppressing(suppressForEmptyList())
        .createTestSuite();
  }

  public Test testsForSingletonList() {
    return ListTestSuiteBuilder.using(