assertThat(units).isEmpty();
  }

  public void testToImmutableEnumSetReused() {
    // The method call lets us capture the accumulator as an A and invoke the callbacks manually
    genericTestToImmutableEnumSetReused(Sets.<SomeEnum>toImmutableEnumSet());
  }

  private static <A extends @Nullable Object> void genericTestToImmutableEnumSetReused(

   * across calls to multiple listeners. Specifically, a given listener will have its callbacks
   * invoked in the same order as the underlying service enters those states. Additionally, at most
   * one of the listener's callbacks will execute at once. However, multiple listeners' callbacks
   * may execute concurrently, and listeners may execute in an order different from the one in which
   * they were registered.

        output.cancel(false);
        throw new MyRuntimeException();
      }
    }
    Fallback fallback = new Fallback();
    SettableFuture<Object> input = SettableFuture.create();

    ListenableFuture<Object> output = catching(input, Throwable.class, fallback, directExecutor());
    fallback.output = output;

    input.setException(new MyException());
    assertTrue(output.isCancelled());
  }

    boolean ran = false;
    @Nullable Callback callback = null;

    public SimpleTearDown() {}

    public SimpleTearDown(Callback callback) {
      this.callback = callback;
    }

    @Override
    public void tearDown() throws Exception {
      if (callback != null) {
        callback.run();
      }
      ran = true;
    }
  }

  }

  /**
   * Streams lines from a URL, stopping when our callback returns false, or we have read all of the
   * lines.
   *
   * @param url the URL to read from
   * @param charset the charset used to decode the input stream; see {@link Charsets} for helpful
   *     predefined constants
   * @param callback the LineProcessor to use to handle the lines
   * @return the output of processing the lines

    listener = new MockFutureListener(resultFuture);
  }

  public void testFutureGetBeforeCallback() throws Exception {
    // Verify that get throws a timeout exception before the callback is called.
    assertThrows(TimeoutException.class, () -> resultFuture.get(1L, TimeUnit.MILLISECONDS));
  }

  public void testFutureGetThrowsWrappedException() throws Exception {
    inputFuture.setException(EXCEPTION);

  public void testOr_supplier_present() {
    assertEquals("a", Optional.of("a").or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_supplier_absent() {
    assertEquals("fallback", Optional.absent().or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_nullSupplier_absent() {

    // instance.  It is always safe to return the same instance because
    // javascript is single-threaded, and only used by blocks that doesn't
    // involve async callbacks.
    return CHAR_BUFFER;
  }

  private Platform() {}

    this.constructions = constructions;
    this.constructionAsymptotics = constructionAsymptotics;
    this.queries = queries;
  }

  /**
   * A Comparable wrapper around a String which executes callbacks on calls to hashCode, equals, and
   * compareTo.
   */
  private static class CountsHashCodeAndEquals implements Comparable<CountsHashCodeAndEquals> {
    private final String delegateString;

           * clearListeners.
           */
          executeListener(task, requireNonNull(curr.executor));
        }
      }
      break;
    }
  }

  /**
   * Callback method that is called exactly once after the future is completed.
   *
   * <p>If {@link #interruptTask} is also run during completion, {@link #afterDone} runs after it.
   *