ListenableFuture<String> f = UncheckedThrowingFuture.throwingError(error);
    MockCallback callback = new MockCallback(error);
    addCallback(f, callback, directExecutor());
  }

  public void testRuntimeExceptionFromGet() {
    RuntimeException e = new IllegalArgumentException("foo not found");
    ListenableFuture<String> f = UncheckedThrowingFuture.throwingRuntimeException(e);