HistoryObserver implements BoardObserver { @Override public void clear() { history.clear(); } HistoryObserver(Board board);  HistoryObserver(CoordinateSystem coords); @Override void clear(); @Override void copyDataFrom(BoardObserver that); short get(int t); int size(); @Override String toString(); @Override void update(StoneColor color, short location,
			ShortList capturedStones);  }
@Test public void testClear() { board.play("c4"); board.play("e1"); board.play("b2"); board.clear(); board.play("a3"); assertEquals(at("a3"), observer.get(0)); }