### Question:
JokerPowerUp implements PowerUp { @Override public void activate(Receptor receptor) { NexusContext context = receptor.getTile().getGrid().getSession().getNexusContext(); context.add(MarbleType.JOKER, MarbleType.JOKER); }  @Override void activate(Receptor receptor);  }### Answer:
@Test public void activate() { receptor.setPowerUp(powerUp); for (Direction direction : Direction.values()) { receptor.accept(direction, new Marble(MarbleType.BLUE)); } verify(context).add(MarbleType.JOKER, MarbleType.JOKER); }