public <E> E invoke(Callable<E> callable) throws ExecutionException, InterruptedException {
    List<E> returnValue = invokeAll(Collections.singletonList(callable));
    return returnValue.get(0);
  }
Testing infrastructure for running code across multiple threads.
jib-core/src/test/java/com/google/cloud/tools/jib/MultithreadedExecutor.java