*
 * <p>If your answers are:
 *
 * <ul>
 *   <li>(1) "no" and (2) "no", use {@link #forGraph(SuccessorsFunction)}.
 *   <li>(1) "yes" and (2) "yes", use {@link #forTree(SuccessorsFunction)}.
 *   <li>(1) "yes" and (2) "no", you can use either, but {@code forTree()} will be more efficient.
 *   <li>(1) "no" and (2) "yes", <b><i>neither will work</i></b>, but if you transform your node
 *       objects into a non-recursive form, you can use {@code forGraph()}.

  }

  public void testIsPresent_no() {
    assertFalse(Optional.absent().isPresent());
  }

  @SuppressWarnings("OptionalOfRedundantMethod") // Unit tests for Optional
  public void testIsPresent_yes() {
    assertTrue(Optional.of("training").isPresent());
  }

  public void testGet_absent() {
    Optional<String> optional = Optional.absent();
    try {
      optional.get();
      fail();

  }

  public void test_contains_null_set_yes() {
    Iterable<@Nullable String> set = Sets.newHashSet("a", null, "b");
    assertTrue(Iterables.contains(set, null));
  }

  public void test_contains_null_set_no() {
    Iterable<String> set = Sets.newHashSet("a", "b");
    assertFalse(Iterables.contains(set, null));
  }

  public void test_contains_null_iterable_yes() {

  }

  private static void assertActuallyTrims(ImmutableDoubleArray iia) {
    ImmutableDoubleArray trimmed = iia.trimmed();
    assertThat(trimmed).isNotSameInstanceAs(iia);

    // Yes, this is apparently how you check array equality in Truth
    assertThat(trimmed.toArray()).isEqualTo(iia.toArray());
  }

  private static void assertDoesntActuallyTrim(ImmutableDoubleArray iia) {

  }

  private static void assertActuallyTrims(ImmutableLongArray iia) {
    ImmutableLongArray trimmed = iia.trimmed();
    assertThat(trimmed).isNotSameInstanceAs(iia);

    // Yes, this is apparently how you check array equality in Truth
    assertThat(trimmed.toArray()).isEqualTo(iia.toArray());
  }

  private static void assertDoesntActuallyTrim(ImmutableLongArray iia) {

  }

  public void testIsPresent_no() {
    assertFalse(Optional.absent().isPresent());
  }

  @SuppressWarnings("OptionalOfRedundantMethod") // Unit tests for Optional
  public void testIsPresent_yes() {
    assertTrue(Optional.of("training").isPresent());
  }

  public void testGet_absent() {
    Optional<String> optional = Optional.absent();
    try {
      optional.get();
      fail();

  }

  private static void assertActuallyTrims(ImmutableLongArray iia) {
    ImmutableLongArray trimmed = iia.trimmed();
    assertThat(trimmed).isNotSameInstanceAs(iia);

    // Yes, this is apparently how you check array equality in Truth
    assertThat(trimmed.toArray()).isEqualTo(iia.toArray());
  }

  private static void assertDoesntActuallyTrim(ImmutableLongArray iia) {

  }

  private static void assertActuallyTrims(ImmutableDoubleArray iia) {
    ImmutableDoubleArray trimmed = iia.trimmed();
    assertThat(trimmed).isNotSameInstanceAs(iia);

    // Yes, this is apparently how you check array equality in Truth
    assertThat(trimmed.toArray()).isEqualTo(iia.toArray());
  }

  private static void assertDoesntActuallyTrim(ImmutableDoubleArray iia) {

        Class<?> theClass = Class.forName(UNSAFE_COMPARATOR_NAME);

        // requireNonNull is safe because the class is an enum.
        Object[] constants = requireNonNull(theClass.getEnumConstants());

        // yes, UnsafeComparator does implement Comparator<byte[]>
        @SuppressWarnings("unchecked")
        Comparator<byte[]> comparator = (Comparator<byte[]>) constants[0];
        return comparator;

  }

  public void test_contains_null_set_yes() {
    Iterable<@Nullable String> set = Sets.newHashSet("a", null, "b");
    assertTrue(Iterables.contains(set, null));
  }

  public void test_contains_null_set_no() {
    Iterable<String> set = Sets.newHashSet("a", "b");
    assertFalse(Iterables.contains(set, null));
  }

  public void test_contains_null_iterable_yes() {