add js-fp3.tests

js-fp3.tests/account.test.js

@@ -0,0 +1,54 @@
+import { describe, it, expect } from 'vitest';
+import { openAccount, withdraw } from '../js-fp3/domain/account.js';
+import { createMoney } from '../js-fp3/domain/money.js';
+
+describe('account domain', () => {
+  it('opening an account with a negative balance returns openingBalanceMustBeNonNegative', () => {
+    const result = openAccount('id-1', createMoney(-1));
+
+    expect(result.error.type).toBe('OpeningBalanceMustBeNonNegative');
+  });
+
+  it('withdrawing a zero amount returns amountMustBePositive', () => {
+    const account = openAccount('id-1', createMoney(100)).value;
+
+    const result = withdraw(account, createMoney(0));
+
+    expect(result.error.type).toBe('AmountMustBePositive');
+  });
+
+  it('withdrawing a negative amount returns amountMustBePositive', () => {
+    const account = openAccount('id-1', createMoney(100)).value;
+
+    const result = withdraw(account, createMoney(-10));
+
+    expect(result.error.type).toBe('AmountMustBePositive');
+  });
+
+  it('withdrawing more than the balance returns insufficientBalance', () => {
+    const account = openAccount('id-1', createMoney(100)).value;
+
+    const result = withdraw(account, createMoney(101));
+
+    expect(result.error.type).toBe('InsufficientBalance');
+  });
+
+  it('insufficientBalance error reports the current balance and attempted amount', () => {
+    const account = openAccount('id-1', createMoney(100)).value;
+
+    const error = withdraw(account, createMoney(150)).error;
+
+    expect(error.type).toBe('InsufficientBalance');
+    expect(error.balance.amount).toBe(100);
+    expect(error.amount.amount).toBe(150);
+  });
+
+  it('successive withdrawals are each applied to the running balance', () => {
+    const account = openAccount('id-1', createMoney(300)).value;
+
+    const updatedAccount1 = withdraw(account, createMoney(100)).value;
+    const updatedAccount2 = withdraw(updatedAccount1, createMoney(100)).value;
+
+    expect(updatedAccount2.balance.amount).toBe(100);
+  });
+});