Initial import of zappier-account-balance from zapier monorepo

test/books.test.js

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+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { AccountBooks, handle } from '../src/books.js';
+import { SUBJECTS } from '../src/subjects.js';
+import { loadInto, saveFrom, booksPath } from '../src/persist.js';
+
+test('adjust credits prepaid and statement lists credits usage payments', () => {
+  const books = new AccountBooks();
+  handle(
+    SUBJECTS.BALANCE_ADJUST,
+    { customerId: 'c1', veraeUserId: 'vu_abc', cents: 500, reason: 'goodwill', agent: 'cs' },
+    books,
+  );
+  handle(SUBJECTS.USAGE_RECORDED, { customerId: 'c1', endpointId: 'timestamp', cents: 4 }, books);
+  handle(SUBJECTS.PAYMENT_RECORDED, { customerId: 'c1', cents: 1000, reason: 'reload' }, books);
+  const st = handle(SUBJECTS.STATEMENT_GET, { customerId: 'c1' }, books);
+  assert.equal(st.prepaidCents, 1496);
+  assert.equal(st.veraeUserId, 'vu_abc');
+  assert.equal(st.credits[0].cents, 500);
+  assert.equal(st.usage[0].endpointId, 'timestamp');
+  assert.equal(st.payments[0].kind, 'payment');
+});
+
+test('customer.put stores display name and lookup by name', () => {
+  const books = new AccountBooks();
+  handle(SUBJECTS.CUSTOMER_PUT, { customerId: 'cust_1', name: 'Ada (free)' }, books);
+  const st = handle(SUBJECTS.STATEMENT_GET, { customerId: 'Ada (free)' }, books);
+  assert.equal(st.customerId, 'cust_1');
+  assert.equal(st.name, 'Ada (free)');
+});
+
+test('persist round-trip keeps prepaid', () => {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'books-'));
+  process.env.BOOKS_PATH = path.join(dir, 'books.json');
+  const a = new AccountBooks();
+  handle(SUBJECTS.BALANCE_ADJUST, { customerId: 'c9', cents: 120, kind: 'reload' }, a);
+  saveFrom(a);
+  assert.ok(fs.existsSync(booksPath()));
+  const b = loadInto(new AccountBooks());
+  assert.equal(b.prepaidCents('c9'), 120);
+  delete process.env.BOOKS_PATH;
+});