Set<String> expected = Collections.singleton("a");
    assertEquals(expected, Optional.of("a").asSet());
  }

  public void testAsSet_absent() {
    assertTrue("Returned set should be empty", Optional.absent().asSet().isEmpty());
  }

  public void testAsSet_presentIsImmutable() {
    Set<String> presentAsSet = Optional.of("a").asSet();
    assertThrows(UnsupportedOperationException.class, () -> presentAsSet.add("b"));
  }

   *
   * <p><b>Note:</b> {@code a.asSet(d).equals(b.asSet(d))} does not imply {@code a.equals(b)}! For
   * example, {@code a} and {@code b} could be {@code [2..4]} and {@code (1..5)}, or the empty
   * ranges {@code [3..3)} and {@code [4..4)}.
   *
   * <p><b>Warning:</b> Be extremely careful what you do with the {@code asSet} view of a large

   * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel
   * edges}, the resulting set will contain at most one edge (equivalent to {@code
   * edgeConnecting(nodeU, nodeV).asSet()}).
   *
   * <p>If either {@code nodeU} or {@code nodeV} are removed from the network after this method is
   * called, the {@code Set} {@code view} returned by this method will be invalidated, and will

   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method has no equivalent in Java 8's
   * {@code Optional} class. However, this common usage:
   *
   * {@snippet :
   * for (Foo foo : possibleFoo.asSet()) {
   *   doSomethingWith(foo);
   * }
   * }
   *
   * ... can be replaced with:
   *
   * {@snippet :
   * possibleFoo.ifPresent(foo -> doSomethingWith(foo));
   * }
   *

    public static Test suite() {
      TestSuite suite = new TestSuite();

      suite.addTest(
          NavigableSetTestSuiteBuilder.using(new ContiguousSetGenerator())
              .named("Range.asSet")
              .withFeatures(
                  CollectionSize.ANY,
                  KNOWN_ORDER,
                  ALLOWS_NULL_QUERIES,
                  NON_STANDARD_TOSTRING,

    public static Test suite() {
      TestSuite suite = new TestSuite();

      suite.addTest(
          NavigableSetTestSuiteBuilder.using(new ContiguousSetGenerator())
              .named("Range.asSet")
              .withFeatures(
                  CollectionSize.ANY,
                  KNOWN_ORDER,
                  ALLOWS_NULL_QUERIES,
                  NON_STANDARD_TOSTRING,