Test blockchain backend

[LLFourn]

Rather than running a regtest node it would be cool if we just had a simulated blockchain that we could do things to from test code.

idea originally from: bitcoindevkit/bdk#446

[casey]

Ideally it would also be fast. We're running tests against regtest nodes, and our main issue is that it's very slow.

[LLFourn]

Happy to mentor someone on this issue if anyone wants to have a shot. It looks like fun!

[casey]

See my comment here: bitcoindevkit/bdk#690 (comment)

TL;DR Maybe we should implement a dummy RPC server instead of a dummy bdk::blockchain::Blockchain?

[danielabrozzoni]

Where we would use this backend, btw? In src/testutils/blockchain_tests.rs, I suppose?

TL;DR Maybe we should implement a dummy RPC server instead of a dummy bdk::blockchain::Blockchain?

Eh, to me it looks more though to implement a dummy RPC server, but I don't really know...

[rajarshimaitra]

One thing I was wondering was, for this to work, we need to mock a considerable portion of bitcoin core's mempool and other behaviors too, if we wanna use it for any meaningful testing situation.. Not sure how difficult or worthwhile its gonna be..

[notmandatory]

@vladimirfomene as we discussed on discord, with the new 1.0 bdk electrum/esplora/rpc clients it's worth taking another look at using a mocking framework instead of or in addition to our current integration tests. One framework that looks like it could do the job is https://docs.rs/mockall/latest/mockall/.

[notmandatory]

Moved to beta release since this is a testing issue. Due to level of work to do this may have to push it out to a post 1.0 release.