Junit test failing for the Observable pattern

I work in a small program using the Observable pattern. The code that I can't modify is provided below.

public abstract class ObservableStock {
    
    private double price;
    private StockType name;
    
    public ObservableStock(StockType name) {
        this.name = name;
    }
    
    protected ObservableStock() {
    }
    
    public StockType getName() {
        return name;
    }
    
    public void setPrice(double price) {
        this.price = price;
    }
    
    public abstract void notifyPriceChange(double price);
    
    public abstract void registerStockExchangeCenter(ObserverStockExchangeCenter oc);
}


public abstract class ObserverStockExchangeCenter {
    
    protected Map<StockType, Double> ownedStock;
    
    public ObserverStockExchangeCenter() {
        this.ownedStock = new HashMap<>();
    }
    
    public void buyStock(ObservableStock s) {
        ownedStock.put(s.getName(), 0.0);
        System.out.println("Helo");
    }
    
    //assume we won't change values in the map
    public Map<StockType, Double> getOwnedStock() {
        return ownedStock;
    }
    
    public abstract void observe(ObservableStock o);
    
    public abstract void notifyChange(StockType type, double price);
}

public enum StockType {
    Amazon,
    Google,
}

I can modify the classes provided below:

public class ObservableStockImpl extends ObservableStock {
    
    private ObserverStockExchangeCenter exchangeCenter;
    public final StockType stockType;
    
    public ObservableStockImpl(StockType name) {
        this.stockType = name;
    }
    
    public void notifyPriceChange(double price) {
        this.exchangeCenter.getOwnedStock().put(stockType, price);
        this.exchangeCenter.notifyChange(stockType, price);
    }
    
    public void registerStockExchangeCenter(ObserverStockExchangeCenter oc) {
        this.exchangeCenter = oc;
    }
    
    public StockType getStockType() {
        return stockType;
    }
}


public class ObserverStockExchangeCenterImpl extends ObserverStockExchangeCenter {
    
    private final List<ObservableStockImpl> observableStocks;
    
    public ObserverStockExchangeCenterImpl() {
        super();
        observableStocks = new ArrayList<>();
    }
    
    public void notifyChange(StockType type, double price) {
        
        for (ObservableStockImpl os : observableStocks) {
            if (os.getStockType().equals(type)) {
                os.setPrice(price);
                os.notifyPriceChange(price);
            }
        }
    }
    
    public void observe(ObservableStock o) {
        observableStocks.add((ObservableStockImpl) o);
    }
    
    @Override
    public void buyStock(ObservableStock s) {
        ObservableStockImpl stock = (ObservableStockImpl) s;
        ownedStock.put(stock.getStockType(), 0.0);
    }
}

However, I failed to pass all the tests which are below:

@Test
public void stockPriceChangeTest(){

    ObservableStock amazonStock = new ObservableStockImpl(StockType.Amazon);
    ObserverStockExchangeCenter NYStockCenter = new ObserverStockExchangeCenterImpl();
    NYStockCenter.buyStock(amazonStock);
    Map<StockType, Double> boughtStocks = NYStockCenter.getOwnedStock();
    assertEquals(1, boughtStocks.size());
    assertEquals(0,boughtStocks.get(StockType.Amazon),0);

    amazonStock.setPrice(5);
    Map<StockType, Double> boughtStocks2 = NYStockCenter.getOwnedStock();
    assertEquals(1, boughtStocks2.size());

    // failing below
    assertEquals(5,boughtStocks2.get(StockType.Amazon),0);
}

The issue is stock price increase not reflected in the code. Can anyone help me to find what is the issue here?