✨ 【第14章 学習用テストと回帰テスト】 Money の変換を行うために無理やりテストを通す

src/__tests__/money.test.ts

@@ -56,3 +56,10 @@ test('test reduce money', () => {
   const result = bank.reduce(Money.dollar(1), 'USD');
   expect(Money.dollar(1)).toEqual(result);
 })
+
+test('test reduce money different currency', () => {
+  const bank = new Bank();
+  bank.addRate('CHF', 'USD', 2);
+  const result = bank.reduce(Money.franc(2), 'USD');
+  expect(Money.dollar(1)).toEqual(result);
+})

src/bank.ts

@@ -5,4 +5,7 @@ export class Bank {
   reduce(source: Expression, to: string):Money {
     return source.reduce(to);
   }
+
+  addRate(from: string, to: string, rate: number) { 
+  }
 }

src/money.ts

@@ -34,6 +34,7 @@ export class Money implements Expression {
   }
 
   reduce(to: string): Money {
-    return this;
+    const rate = this.currency === 'CHF' && to === 'USD' ? 2 : 1;
+    return new Money(this.amount / rate, to)
   }
 }