test: harden business boundary conditions

apps/server/src/wallets/wallets.service.spec.ts

@@ -50,3 +50,70 @@ describe('WalletsService payment rules', () => {
     expect(ctx.saved.some((row) => row.type === 'bill_refund' && Number(row.amount) === 40)).toBe(true);
   });
 });
+
+describe('WalletsService financial boundaries', () => {
+  it('caps a debit at total minus already paid even when outstandingAmount is stale', async () => {
+    const ctx = manager(50);
+    const service = new WalletsService({} as any, {} as any, {} as any, {} as any);
+    const bill = {
+      id: 10,
+      studentId: 10,
+      totalAmount: 100,
+      paidAmount: 90,
+      outstandingAmount: 100,
+      status: 'partially_paid',
+    } as Bill;
+
+    await service.debitBill(ctx.value as any, bill);
+
+    expect(bill).toMatchObject({ paidAmount: 100, outstandingAmount: 0, status: 'paid' });
+    expect(ctx.wallet.balance).toBe(40);
+    expect(ctx.saved.some((row) => row.type === 'bill_payment' && row.amount === -10)).toBe(true);
+  });
+
+  it('caps a refund at the bill total when paidAmount is corrupt', async () => {
+    const ctx = manager(10);
+    const service = new WalletsService({} as any, {} as any, {} as any, {} as any);
+    const bill = {
+      id: 11,
+      studentId: 10,
+      totalAmount: 100,
+      paidAmount: 150,
+      outstandingAmount: 0,
+      status: 'paid',
+    } as Bill;
+
+    await service.refundBill(ctx.value as any, bill, '冲正');
+
+    expect(ctx.wallet.balance).toBe(110);
+    expect(ctx.saved.some((row) => row.type === 'bill_refund' && row.amount === 100)).toBe(true);
+  });
+
+  it('does not issue a second refund for an already cancelled bill', async () => {
+    const ctx = manager(10);
+    const service = new WalletsService({} as any, {} as any, {} as any, {} as any);
+    const bill = {
+      id: 12,
+      studentId: 10,
+      totalAmount: 100,
+      paidAmount: 100,
+      outstandingAmount: 0,
+      status: 'cancelled',
+    } as Bill;
+
+    await service.refundBill(ctx.value as any, bill, '重复取消');
+
+    expect(ctx.wallet.balance).toBe(10);
+    expect(ctx.saved).toHaveLength(0);
+  });
+
+  it('rejects an amount that rounds to zero before opening a transaction', async () => {
+    const dataSource = { transaction: jest.fn() };
+    const service = new WalletsService({} as any, {} as any, {} as any, dataSource as any);
+
+    await expect(service.changeBalance({ studentId: 1, amount: 0.004, type: 'adjustment' })).rejects.toBeInstanceOf(
+      BadRequestException,
+    );
+    expect(dataSource.transaction).not.toHaveBeenCalled();
+  });
+});