private static final class TestFuture {

    final ListenableFuture<String> future;
    final String name;
    final Runnable finisher;

    TestFuture(ListenableFuture<String> future, String name, Runnable finisher) {
      this.future = future;
      this.name = name;
      this.finisher = finisher;
    }
  }

  /**

  private static final class TestFuture {

    final ListenableFuture<String> future;
    final String name;
    final Runnable finisher;

    TestFuture(ListenableFuture<String> future, String name, Runnable finisher) {
      this.future = future;
      this.name = name;
      this.finisher = finisher;
    }
  }

  /**

   *                 return countDifferentLines(file1Reader, file2Reader);
   *               },
   *               executor)
   *           .closing(executor);
   * }</pre>
   */
  // TODO(cpovirk): Use simple name instead of fully qualified after we stop building with JDK 8.
  @com.google.errorprone.annotations.DoNotMock(
      "Use ClosingFuture.whenAllSucceed() or .whenAllComplete() instead.")
  public static class Combiner {

    return new TreeMap<>();
  }

  /**
   * Creates a <i>mutable</i> {@code TreeMap} instance with the same mappings as the specified map
   * and using the same ordering as the specified map.
   *
   * <p><b>Note:</b> if mutability is not required, use {@link
   * ImmutableSortedMap#copyOfSorted(SortedMap)} instead.
   *