test: harden business boundary conditions

apps/server/src/deposits/deposits.boundaries.spec.ts

@@ -0,0 +1,53 @@
+import { BadRequestException } from '@nestjs/common';
+import { DepositsService } from './deposits.service';
+import { Deposit } from '../entities/deposit.entity';
+
+function serviceWith(deposit?: Partial<Deposit>) {
+  const record = deposit ? ({ id: 1, studentId: 2, ...deposit } as Deposit) : null;
+  const repo = {
+    findOne: jest.fn(async (options: any) => options?.where?.studentId ? record : record),
+    create: jest.fn((value) => value),
+    save: jest.fn(async (value) => value),
+  };
+  const installmentRepo = {
+    create: jest.fn((value) => value),
+    save: jest.fn(async (value) => value),
+  };
+  const studentRepo = { findOne: jest.fn().mockResolvedValue({ id: 2 }) };
+  return { service: new DepositsService(repo as any, installmentRepo as any, studentRepo as any), repo, installmentRepo };
+}
+
+describe('DepositsService boundaries', () => {
+  it('rejects an installment amount that rounds to zero', async () => {
+    const { service, installmentRepo } = serviceWith({ amount: 500, status: 'paid' });
+
+    await expect(service.addInstallment(1, 0.004, '2026-08-01')).rejects.toBeInstanceOf(BadRequestException);
+    expect(installmentRepo.save).not.toHaveBeenCalled();
+  });
+
+  it('rejects a repeated full refund', async () => {
+    const { service, repo } = serviceWith({ amount: 0, status: 'refunded' });
+
+    await expect(service.refund(1, { refundDate: '2026-07-14' })).rejects.toBeInstanceOf(BadRequestException);
+    expect(repo.save).not.toHaveBeenCalled();
+  });
+
+  it('rounds cumulative collections and clears stale refund audit fields', async () => {
+    const { service } = serviceWith({
+      amount: 10.01,
+      status: 'refunded',
+      refundDate: '2026-07-01',
+      refundAmount: 5,
+      refundedBy: 9,
+      refundedAt: new Date(),
+    });
+
+    const result = await service.create({ studentId: 2, amount: 0.02, paidDate: '2026-07-14' }, 7);
+
+    expect(result).toMatchObject({ amount: 10.03, status: 'paid', recordedBy: 7 });
+    expect(result.refundDate).toBeNull();
+    expect(result.refundAmount).toBeNull();
+    expect(result.refundedBy).toBeNull();
+    expect(result.refundedAt).toBeNull();
+  });
+});