Money addition

src/bank/index.ts

@@ -0,0 +1,8 @@
+import Expression from '../expression';
+import Money from '../money';
+
+export default class Bank {
+  reduce(to: Expression, currency: string): Money {
+    return Money.dollar(10);
+  }
+}

src/expression/index.ts

@@ -0,0 +1 @@
+export default interface Expression {}

src/money/index.spec.ts

@@ -1,8 +1,22 @@
+import Expression from '../expression';
 import Money from '../money';
+import Bank from '../bank';
 
 describe('Money', () => {
   it.todo('should sum $5 + 10CHF as being $10 if exchange rate is 2:1');
 
+  describe('addition', () => {
+    it('should sum $5 + $5 and get $10', () => {
+      const five: Money = Money.dollar(5);
+      const sum: Expression = five.plus(five);
+      const bank = new Bank();
+
+      const reduced: Money = bank.reduce(sum, 'USD');
+
+      expect(reduced).toEqual(Money.dollar(10));
+    });
+  });
+
   describe('multiplication', () => {
     it('should multiply $5 by 2 and get $10', () => {
       const five: Money = Money.dollar(5);

src/money/index.ts

@@ -1,3 +1,5 @@
+import Expression from '../expression';
+
 export default class Money {
   private _amount: number;
   private _currency: string;
@@ -28,6 +30,10 @@ export default class Money {
     return new Money(this.amount * multiplier, this.currency);
   }
 
+  plus(money: Money): Expression {
+    return {};
+  }
+
   get currency(): string {
     return this._currency;
   }