Wraps Stripe API testing patterns: test-mode initialization, the canonical test cards (4242 success; 4000 0000 0000 0002 declined; 4000 0027 6000 3184 3DS challenge per 3ds-test-flow-reference), the Stripe CLI webhook flow (`stripe listen --forward-to`), the Stripe CLI fixture commands (`stripe trigger payment_intent.succeeded`), and the webhook signature verification (Stripe-Signature header + HMAC-SHA256). Use when testing Stripe-integrated code.