Next.js Test Writer

Prompt: “Here is a small feature from our Next.js App Router app. Plan the tests and write them, and present the plan and every test file in a single HTML page. lib/coupon.ts: export type Coupon = { code: string; percentOff: number; expiresAt: string; maxRedemptions: number; redemptions: number; firstOrderOnly: boolean }; export function applyCoupon(c: Coupon, subtotalCents: number, now: Date, isFirstOrder: boolean) { if (new Date(c.expiresAt) < now) return { ok: false, reason: "expired" } as const; if (c.redemptions >= c.maxRedemptions) return { ok: false, reason: "used_up" } as const; if (c.firstOrderOnly && !isFirstOrder) return { ok: false, reason: "first_order_only" } as const; const discount = Math.round(subtotalCents * c.percentOff / 100); return { ok: true, totalCents: subtotalCents - discount, discountCents: discount } as const; } app/api/coupons/apply/route.ts: import { NextResponse } from "next/server"; import { getCoupon, isFirstOrder } from "@/lib/db"; import { applyCoupon } from "@/lib/coupon"; export async function POST(req: Request) { const { code, subtotalCents, userId } = await req.json(); if (!code || typeof subtotalCents !== "number") return NextResponse.json({ error: "code and subtotalCents are required" }, { status: 400 }); const coupon = await getCoupon(code.trim().toUpperCase()); if (!coupon) return NextResponse.json({ error: "not_found" }, { status: 404 }); const result = applyCoupon(coupon, subtotalCents, new Date(), await isFirstOrder(userId)); return NextResponse.json(result, { status: result.ok ? 200 : 422 }); } app/checkout/CouponForm.tsx is a client component with a text input labeled "Coupon code", an "Apply" button, and it shows the new total or an error message from the API.” Run on claude-opus-5-5. 3 independent runs per side; all are shown, none picked by hand.