springframeworkguru#29 - TDD Chapter 13 - Make It - Implement Bank.reduce method - Strange code!

Author: patrickcorbett

src/main/java/guru/springframework/Bank.java

@@ -2,6 +2,6 @@
 
 public class Bank {
     public Money reduce(Expression source, String toCurrency) {
-        return Money.dollar(10);
+        return source.reduce(toCurrency);
     }
 }

src/main/java/guru/springframework/Expression.java

@@ -1,4 +1,5 @@
 package guru.springframework;
 
 public interface Expression {
+    Money reduce(String to);
 }

src/main/java/guru/springframework/Money.java

@@ -36,6 +36,11 @@ public boolean equals(Object object) {
         return amount == money.amount && this.currency.equals(money.currency);
     }
 
+    @Override
+    public Money reduce(String to){
+        return this;
+    }
+
     @Override
     public String toString() {
         return "Money{" +
@@ -54,7 +59,7 @@ public Money times(int multiplier) {
         return new Money(amount * multiplier, this.currency);
     }
 
-    public Expression plus(int amount) {
-        return new Money(this.amount + amount, this.currency);
+    public Expression plus(Money addend) {
+        return new Sum(this, addend);
     }
 }

src/main/java/guru/springframework/Sum.java

@@ -0,0 +1,16 @@
+package guru.springframework;
+
+public class Sum implements Expression {
+    Money augmend;
+    Money addmend;
+
+    public Sum(Money augmend, Money addmend) {
+        this.augmend = augmend;
+        this.addmend = addmend;
+    }
+
+    public Money reduce(String toCurrency){
+        int amount = augmend.amount + addmend.amount;
+        return new Money(amount, toCurrency);
+    }
+}

src/test/java/guru/springframework/MoneyTest.java

@@ -35,11 +35,35 @@ void testCurrency() {
     }
 
     @Test
-    void testAddition() {
+    void testSimpleAddition() {
         Money five = Money.dollar(5);
-        Expression sum = five.plus(5);
+        Expression sum = five.plus(five);
         Bank bank = new Bank();
         Money reduced = bank.reduce(sum, "USD");
         assertEquals(Money.dollar(10), reduced);
     }
+
+    @Test
+    void testPlusReturnsSum() {
+        Money five = Money.dollar(5);
+        Expression result = five.plus(five);
+        Sum sum = (Sum) result;
+        assertEquals(five, sum.augmend);
+        assertEquals(five, sum.addmend);
+    }
+
+    @Test
+    void testReduceSum() {
+        Expression sum = new Sum(Money.dollar(3), Money.dollar(4));
+        Bank bank = new Bank();
+        Money result = bank.reduce(sum, "USD");
+        assertEquals(Money.dollar(7), result);
+    }
+
+    @Test
+    void testReduceMoney() {
+        Bank bank = new Bank();
+        Money result = bank.reduce(Money.dollar(1), "USD");
+        assertEquals(Money.dollar(1), result);
+    }
 }