How do you test payment webhook edge cases?

I work at a PSP. We recently had a production bug where a payment succeeded but our system didn't update — the webhook was delayed 45 seconds. Stripe's test mode doesn't simulate delays, timeouts, or webhook failures. We ended up writing internal mocks, but it's tedious. Considering building a simple tool: configurable delays, webhook failure simulation, request timeline. Curious how others handle this. Do you just write custom mocks? Accept the risk? Use something I don't know about?