Take a look at the deduct method in the Creditor class. Pay attention to the NotEnoughFundsException that is thrown.

package com.teamtreehouse.vending;

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

import static org.junit.Assert.*;

public class CreditorTest {

    private Creditor creditor;

   @Before
    public void setUp() throws Exception {
        creditor = new Creditor();
    }

    @Test
   (expected = ...)
    public void addingFundsIncrementsAvailableFunds() throws Exception {
        creditor.addFunds(25);
        creditor.addFunds(25);

        assertEquals(50, creditor.getAvailableFunds());
    }

    @Test
  (expected = ...)
    public void refundingReturnsAllAvailableFunds() throws Exception {
        creditor.addFunds(10);

        int refund = creditor.refund();

        assertEquals(10, refund);
    }

    @Test
  (expected = ...)
    public void refundingResetsAvailableFundsToZero() throws Exception {
        creditor.addFunds(10);

        creditor.refund();

        assertEquals(0, creditor.getAvailableFunds());
    }

}

package com.teamtreehouse.vending;

public class Creditor {
    private int funds;

    public Creditor() {
        funds = 0;
    }

    public void addFunds(int money) {
        funds += money;
    }

    public void deduct(int money) throws NotEnoughFundsException {
        if (money > funds) {
            throw new NotEnoughFundsException();
        }
        funds -= money;
    }

    public int refund() {
        int refund = funds;
        funds = 0;
        return refund;
    }

    public int getAvailableFunds() {
        return funds;
    }

}

package com.teamtreehouse.vending;

public class NotEnoughFundsException extends Exception {
}