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# V1

- Create project TestInfected
- Add new TestCase class MoneyTest
  - package Money
- add JUnit 4 to project

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	package money;

	import static org.junit.Assert.*;
	import org.junit.*;

	public class MoneyTest {
		// fixtures
		private Money f12CHF;
		private Money f14CHF;

		@Before public void setUp() {
			f12CHF = new Money(12, "CHF");
			f14CHF = new Money(14, "CHF");
		}

		@Test public void testEquals() {
			assertNotNull(f12CHF);
			assertEquals(f12CHF, f12CHF);
			assertEquals(f12CHF, new Money(12, "CHF"));
			assertFalse(f12CHF.equals(f14CHF));
		}

		@Test public void testSimpleAdd() {
			Money expected = new Money(26, "CHF");
			Money result = f12CHF.add(f14CHF);
			assertEquals(expected, result);
		}
	}

---
- Eclipse suggests to create Money class
- Add the class; add methods till the test runs

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	package money;

	public class Money {
		final int amount; // NB: package scope
		final String currency;

		public Money(int amount, String currency) {
			this.amount = amount;
			this.currency = currency;
			assert invariant();
		}

		protected boolean invariant() {
			return amount > 0;
		}

		public Money add(Money other) {
			assert this.currency.equals(other.currency);
			return new Money(amount + other.amount, currency);
		}

		public boolean equals(Object anObject) {
			if (anObject instanceof Money) {
				Money other = (Money) anObject;
				return (amount == other.amount)
					&& (currency == other.currency);
			} else {
				return false;
			}
		}
	
		public int hashCode() {
			return currency.hashCode();
		}
	}

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# V2
- Add new MoneyTest tests

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	public class MoneyTest {
	...

		private Money f7USD;
		private Money f21USD;
		private MoneyBag fMB1;
		private MoneyBag fMB2;
	
		@Before public void setUp() {
			...
			f7USD =	new Money( 7, "USD");
			f21USD = new Money(21, "USD");
			fMB1 = new MoneyBag(f12CHF, f7USD);
			fMB2 = new MoneyBag(f14CHF, f21USD);
		}
	
		...

		@Test public void testBagEquals() {
			assertNotNull(fMB1);
			assertEquals(fMB1, fMB1);
			assertFalse(fMB1.equals(f12CHF));
			assertFalse(f12CHF.equals(fMB1));
			assertFalse(fMB1.equals(fMB2));
		}
	}

---
- Create MoneyBag
- Add constructor ...

---

	package money;
	import java.util.Hashtable;

	public class MoneyBag {

		private Hashtable<String,Money> monies = new Hashtable<String,Money>(5);

		MoneyBag(Money m1, Money m2) {
			appendMoney(m1);
			appendMoney(m2);
			assert invariant();
		}

		MoneyBag(Money bag[]) {
			for (Money money : bag) {
				appendMoney(money);
			}
			assert invariant();
		}

		protected boolean invariant() {
			return monies.size() > 1;
		}

		private void appendMoney(Money money) {
			Money m = (Money) monies.get(money.currency);
			if (m != null) {
				m = m.add(money);
			} else {
				m = money;
			}
			monies.put(money.currency, m);
		}
	}

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# V3
- Add new MoneyTest cases

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	public class MoneyTest extends TestCase {
		...
		@Test public void testMixedSimpleAdd() {
			// [12 CHF] + [7 USD] == {[12 CHF][7 USD]}
			Money bag[] = { f12CHF, f7USD };
			MoneyBag expected = new MoneyBag(bag);
			assertEquals(expected, f12CHF.add(f7USD));
		}
	}

---
- Add IMoney interface

---

	public interface IMoney {
		public IMoney add(IMoney aMoney);
		// NB: the following have package scope only
		IMoney addMoney(Money aMoney);
		IMoney addMoneyBag(MoneyBag aMoneyBag);
	}

---
- Let Money implement IMoney
- Add unimplemented methods

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	package money.v3;

	class Money implements IMoney {
		...
		// Replace: public Money add(...)

		public IMoney add(IMoney m) {
			return m.addMoney(this);
		}

		public IMoney addMoney(Money m) {
			if (m.currency.equals(currency) ) {
				return new Money(amount+m.amount, currency);
			}
			return new MoneyBag(this, m);
		}

		public IMoney addMoneyBag(MoneyBag s) {
			return s.addMoney(this);
		}
	}

---
- Let MoneyBag implement IMoney
- Add missing methods

---

	class MoneyBag implements IMoney {
		...

		private void appendMoney(Money aMoney) {
			Money m = monies.get(aMoney.currency);
			if (m != null) {
				m = (Money) m.add(aMoney); // add downcast
			} else {
				m = aMoney;
			}
			monies.put(aMoney.currency, m);
		}

		MoneyBag(Money m, MoneyBag bag) {
			appendMoney(m);
			appendBag(bag);
			assert invariant();
		}

		MoneyBag(MoneyBag m1, MoneyBag m2) {
			appendBag(m1);
			appendBag(m2);
			assert invariant();
		}

		public IMoney add(IMoney m) {
			return m.addMoneyBag(this);
		}

		public IMoney addMoney(Money m) {
			return new MoneyBag(m, this);
		}

		public IMoney addMoneyBag(MoneyBag s) {
			return new MoneyBag(s, this);
		}

		private void appendBag(MoneyBag aBag) {
			for (Money m: monies.values()) {
				appendMoney(m);
			}
		}
	}

---
- Test still broken

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# V4

---
- Add MoneyBag.equals

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	class MoneyBag implements IMoney {
		...

		public boolean equals(Object anObject) {
			if (!(anObject instanceof MoneyBag)) {
				return false;
			}
			Set<Money> myMoneySet = new HashSet<Money>(monies.values());
			MoneyBag other = (MoneyBag) anObject;
			Set<Money> otherMoneySet = new HashSet<Money>(other.monies.values());
			return myMoneySet.equals(otherMoneySet);
		}
	
		public int hashCode() {
			return monies.hashCode();
		}
	}

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