private static class Prepender {

    private final String prefix;
    private final int times;

    Prepender(@NotBlank @Nullable String prefix, int times) throws NullPointerException {
      this.prefix = prefix;
      this.times = times;
    }

    Prepender(String... varargs) {
      this(null, 0);
    }

    // just for testing

        "Should be able to peek() first element multiple times", "A", peekingIterator.peek());
    assertEquals(
        "next() should still return first element after peeking", "A", peekingIterator.next());

    assertEquals("Should be able to peek() at middle element", "B", peekingIterator.peek());
    assertEquals(
        "Should be able to peek() middle element multiple times", "B", peekingIterator.peek());
    assertEquals(

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import junit.framework.TestCase;

/**
 * Tests relating to cache expiration: make sure entries expire at the right times, make sure
 * expired entries don't show up, etc.
 *
 * @author mike nonemacher
 */
@SuppressWarnings("deprecation") // tests of deprecated method
public class CacheExpirationTest extends TestCase {

        Guava's main yardstick for evaluating proposed features can be summed up as [utility times
        ubiquity](https://github.com/google/guava/wiki/PhilosophyExplained#utility-times-ubiquity).


        #### Utility: compare with alternatives


        There is always *some* alternative to adding a new feature to Guava, even if it's just

   * features to support (from the enclosing {@link AbstractIteratorTester} instance). Instead of
   * throwing exceptions like {@link NoSuchElementException} at the appropriate times, it throws
   * {@link PermittedMetaException} instances, which wrap a set of all exceptions that the iterator
   * could throw during the invocation of that method. This is necessary because, e.g., a call to

      Subscriber that = (Subscriber) obj;
      // Use == so that different equal instances will still receive events.
      // We only guard against the case that the same object is registered
      // multiple times
      return target == that.target && method.equals(that.method);
    }
    return false;
  }

  /**
   * Checks whether {@code method} is thread-safe, as indicated by the presence of the {@link

   * escaping for code points if required.
   *
   * <p>Note that arrays returned by this method must not be modified once they have been returned.
   * However it is acceptable to return the same array multiple times (even for different input
   * characters).
   *
   * @param cp the Unicode code point to escape
   * @return the replacement characters, or {@code null} if no escaping was required
   */
  @CheckForNull

            }
          }
        }
        if (done) {
          break;
        }
      }
    }
  }

  /**
   * Multiple threads using same array of counters successfully update a number of times equal to
   * total count
   */
  public void testCountingInMultipleThreads() throws InterruptedException {
    final AtomicDoubleArray aa = new AtomicDoubleArray(SIZE);
    for (int i = 0; i < SIZE; i++) {

   * node(s) to any node may lead to:
   *
   * <ul>
   *   <li>Traversal not terminating (if the graph has cycles)
   *   <li>Nodes being visited multiple times (if multiple paths exist from any start node to any
   *       node reachable from any start node)
   * </ul>
   *
   * <p><b>Performance notes</b>
   *
   * <ul>

            return null;
          }
        });

    assertEquals(incrementByNanos * numberOfThreads, ticker.read());
  }

  /** Runs {@code callable} concurrently {@code numberOfThreads} times. */
  @GwtIncompatible // concurrency
  private void runConcurrentTest(int numberOfThreads, final Callable<@Nullable Void> callable)
      throws Exception {