Can't seem to finish the challenge

package com.teamtreehouse.vending;

import org.junit.Before;
import org.junit.Test;

import static org.junit.Assert.*;

public class VendingMachineTest {
    private VendingMachine machine;

    public class NotifierSub implements Notifier {

        @Override
        public void onSale(Item item) {
            return;
        }
    }

    @Before
    public void setUp() throws Exception {
        Notifier notifier = new NotifierSub();
        machine = new VendingMachine(notifier, 10, 10, 10);
        machine.restock("A1", "Twinkies", 10, 30, 75);
    }

    @Test
    public void vendingWhenStockedReturnsItem() throws Exception {
        machine.addMoney(75);

        Item item = machine.vend("A1");

        assertEquals("Twinkies", item.getName());
    }

  @Test
  public void onSuccessfulVendItemTotalIsIncremented(){
   machine.vend("A1");
    assertEquals(1, machine.getRunningSalesTotal());
  }
}

package com.teamtreehouse.vending;


public class VendingMachine {
    private final Notifier notifier;
    private final AbstractChooser chooser;
    private final Creditor creditor;
    private final Bin[][] bins;
    private int runningSalesTotal;

    public VendingMachine(Notifier notifier, int rowCount, int columnCount, int maxItemsPerBin) {
        this.notifier = notifier;
        chooser = new AlphaNumericChooser(rowCount, columnCount);
        creditor = new Creditor();
        runningSalesTotal = 0;
        bins = new Bin[rowCount][columnCount];
        for (int row = 0; row < rowCount; row++) {
            for (int col = 0; col < columnCount; col++) {
                bins[row][col] = new Bin(maxItemsPerBin);
            }
        }
    }

    public void addMoney(int money) {
        creditor.addFunds(money);
    }

    public int refundMoney() {
        return creditor.refund();
    }

    public Item vend(String input) throws InvalidLocationException, NotEnoughFundsException {
        Bin bin = binByInput(input);
        int price = bin.getItemPrice();
        creditor.deduct(price);
        runningSalesTotal += price;
        Item item = bin.release();
        notifier.onSale(item);
        return item;
    }

    public int getRunningSalesTotal() {
        return runningSalesTotal;
    }

    public void restock(String input, String name, int amount, int wholesalePrice, int retailPrice) throws InvalidLocationException {
        Bin bin = binByInput(input);
        bin.restock(name, amount, wholesalePrice, retailPrice);
    }

    private Bin binByInput(String input) throws InvalidLocationException {
        AbstractChooser.Location location = chooser.locationFromInput(input);
        return bins[location.getRow()][location.getColumn()];
    }

}