Add testnet tests #886
Description
Task description
Add tests which involve interacting with the canonical testnet
Context
Some issues don't occur in regtest scenarios. Examples of things a testnet test might catch are issues that come up with sync speed/memory usage (where a chain of 1,000,000+ blocks can stress-test), as well as edge-cases we might not think of that come up occasionally on live networks.
Acceptance criteria
Runnable tests which sync testnet or a large chunk of it, and make some assertions about correctly syncing/serving that data.
Area
No response