public static <E> ImmutableSet<E> of() {
    return (ImmutableSet<E>) RegularImmutableSet.EMPTY;
  }

  /**
   * Returns an immutable set containing the given element. Preferred over {@link
   * Collections#singleton} for code consistency, {@code null} rejection, and because the return
   * type conveys the immutability guarantee.
   */
  public static <E> ImmutableSet<E> of(E e1) {

    @Override
    protected Set<String> create(String[] elements) {
      return ImmutableSet.copyOf(elements);
    }
  }

  public static class ImmutableSetUnsizedBuilderGenerator extends TestStringSetGenerator {
    @Override
    protected Set<String> create(String[] elements) {
      ImmutableSet.Builder<String> builder = ImmutableSet.builder();
      for (String e : elements) {
        builder.add(e);
      }

          // All collections are immutable empty. So safe for any type parameter.
          .put(Iterator.class, ImmutableSet.of().iterator())
          .put(PeekingIterator.class, peekingIterator(ImmutableSet.of().iterator()))
          .put(ListIterator.class, ImmutableList.of().listIterator())
          .put(Iterable.class, ImmutableSet.of())
          .put(Collection.class, ImmutableList.of())

    assertThat(graph.nodes()).contains(N1);
  }

  @Test
  public void addNode_existingNode() {
    assume().that(graphIsMutable()).isTrue();

    addNode(N1);
    ImmutableSet<Integer> nodes = ImmutableSet.copyOf(graph.nodes());
    assertThat(graphAsMutableGraph.addNode(N1)).isFalse();
    assertThat(graph.nodes()).containsExactlyElementsIn(nodes);
  }

  @Test

    Hasher hasher2 = hashFunction.newHasher();
    for (int i = 0; i < numActions; i++) {
      RandomHasherAction.pickAtRandom(random1).performAction(random1, ImmutableSet.of(hasher1));
      RandomHasherAction.pickAtRandom(random2).performAction(random2, ImmutableSet.of(hasher2));
    }

    Assert.assertEquals(expected1, hasher1.hash());
    Assert.assertEquals(expected2, hasher2.hash());
  }

/**
 * Tests for the MacHashFunction.
 *
 * @author Kurt Alfred Kluever
 */
@NullUnmarked
public class MacHashFunctionTest extends TestCase {

  private static final ImmutableSet<String> INPUTS = ImmutableSet.of("", "Z", "foobar");

  private static final SecretKey MD5_KEY =
      new SecretKeySpec("secret key".getBytes(UTF_8), "HmacMD5");
  private static final SecretKey SHA1_KEY =

        .addEqualityGroup(ImmutableSet.of(), ImmutableSet.of())
        .addEqualityGroup(ImmutableSet.of(1), ImmutableSet.of(1), ImmutableSet.of(1, 1))
        .addEqualityGroup(ImmutableSet.of(1, 2, 1), ImmutableSet.of(2, 1, 1))
        .testEquals();
  }

  @GwtIncompatible("internals")
  public void testControlsArraySize() {
    ImmutableSet.Builder<String> builder = new ImmutableSet.Builder<String>();

  static final Iterable<Double> ALL_DOUBLE_CANDIDATES;
  static final Iterable<Double> DOUBLE_CANDIDATES_EXCEPT_NAN;

  static {
    ImmutableSet.Builder<Double> integralBuilder = ImmutableSet.builder();
    ImmutableSet.Builder<Double> fractionalBuilder = ImmutableSet.builder();
    integralBuilder.addAll(Doubles.asList(0.0, -0.0, Double.MAX_VALUE, -Double.MAX_VALUE));
    // Add small multiples of MIN_VALUE and MIN_NORMAL

  }

  public void testCreate_empty() {
    assertEquals(ImmutableSet.of(), ContiguousSet.create(Range.closedOpen(1, 1), integers()));
    assertEquals(ImmutableSet.of(), ContiguousSet.closedOpen(1, 1));
    assertEquals(ImmutableSet.of(), ContiguousSet.create(Range.openClosed(5, 5), integers()));
    assertEquals(
        ImmutableSet.of(), ContiguousSet.create(Range.lessThan(Integer.MIN_VALUE), integers()));
    assertEquals(

          ImmutableList.Builder::combine,
          ImmutableList.Builder::build);

  private static final Collector<Object, ?, ImmutableSet<Object>> TO_IMMUTABLE_SET =
      Collector.of(
          ImmutableSet::builder,
          ImmutableSet.Builder::add,
          ImmutableSet.Builder::combine,
          ImmutableSet.Builder::build);

  @GwtIncompatible
  private static final Collector<Range<Comparable<?>>, ?, ImmutableRangeSet<Comparable<?>>>