/** Stub: responde siempre el mismo stock, sin base de datos ni inventario. */
public class FixedStockLevels implements StockLevels {
    private final int units;

    public FixedStockLevels(int units) {
        this.units = units;
    }

    @Override
    public int unitsOf(String product) {
        return units;
    }
}