Iterator<String> iterator = singletonList("foo").iterator();
    assertEquals("foo", getOnlyElement(iterator));
  }

  public void testGetOnlyElement_noDefault_empty() {
    Iterator<String> iterator = emptyIterator();
    assertThrows(NoSuchElementException.class, () -> getOnlyElement(iterator));
  }

  public void testGetOnlyElement_noDefault_moreThanOneLessThanFiveElements() {

    Iterator<String> iterator = singletonList("foo").iterator();
    assertEquals("foo", getOnlyElement(iterator));
  }

  public void testGetOnlyElement_noDefault_empty() {
    Iterator<String> iterator = emptyIterator();
    assertThrows(NoSuchElementException.class, () -> getOnlyElement(iterator));
  }

  public void testGetOnlyElement_noDefault_moreThanOneLessThanFiveElements() {

    @SuppressWarnings("unchecked") // super interface type of T
    Class<? super T> interfaceType =
        (Class<? super T>) Iterables.getOnlyElement(Arrays.asList(forwarderClass.getInterfaces()));
    new ForwardingWrapperTester()
        .testForwarding(
            interfaceType,
            new Function<Object, T>() {
              @Override

  }

  public void testGetOnlyElement_withDefault_singleton() {
    Iterable<String> iterable = singletonList("foo");
    assertEquals("foo", getOnlyElement(iterable, "bar"));
  }

  public void testGetOnlyElement_withDefault_empty() {
    Iterable<String> iterable = emptyList();
    assertEquals("bar", getOnlyElement(iterable, "bar"));
  }

   * @throws IllegalArgumentException if the iterable contains multiple elements
   */
  @ParametricNullness
  public static <T extends @Nullable Object> T getOnlyElement(Iterable<T> iterable) {
    return Iterators.getOnlyElement(iterable.iterator());
  }

  /**
   * Returns the single element contained in {@code iterable}, or {@code defaultValue} if the
   * iterable is empty.
   *

    List<Future<String>> results;

    results = service.invokeAll(callables);
    assertThat(getOnlyElement(results)).isInstanceOf(TrustedListenableFutureTask.class);

    results = service.invokeAll(callables, 1, SECONDS);
    assertThat(getOnlyElement(results)).isInstanceOf(TrustedListenableFutureTask.class);

    /*
     * TODO(cpovirk): move ForwardingTestCase somewhere common, and use it to

    List<Future<String>> results;

    results = service.invokeAll(callables);
    assertThat(getOnlyElement(results)).isInstanceOf(TrustedListenableFutureTask.class);

    results = service.invokeAll(callables, 1, SECONDS);
    assertThat(getOnlyElement(results)).isInstanceOf(TrustedListenableFutureTask.class);

    /*
     * TODO(cpovirk): move ForwardingTestCase somewhere common, and use it to

 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.Iterables.getOnlyElement;
import static com.google.common.collect.Tables.immutableCell;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

import static com.google.common.base.Preconditions.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.Iterables.getOnlyElement;
import static com.google.common.collect.Iterators.emptyIterator;
import static com.google.common.collect.SortedLists.KeyAbsentBehavior.NEXT_HIGHER;

    IllegalStateException ex = new IllegalStateException(re);

    assertThat(getCausalChain(ex)).containsExactly(ex, re, iae, sue).inOrder();
    assertSame(sue, Iterables.getOnlyElement(getCausalChain(sue)));

    List<Throwable> causes = getCausalChain(ex);
    assertThrows(UnsupportedOperationException.class, () -> causes.add(new RuntimeException()));
  }