Problem: no testnet compatibility tests

[tomtau]

as there's already a public testnet running (on top of unreleased SDK version), it'll be good to find out early if something broke with a simple dependency upgrade (and one needs to trigger some network upgrade proposal and/or provide some conversion tools), so this includes:

1. parsing genesis.json
2. processing block data / transactions -- (either from network or reading data persisted by the old binary)
3. external API changes

[yihuang]

I guess we can make an integration test case to join the running testnet with recent binary. and issue a warning if it don't work.

[yihuang]

https://github.com/cosmos/cosmos-sdk/pull/7526/files#diff-046f100a1eb97e25aa6ecc5b5a618c222775184faf805d7a7cbb9e9e6a92aba1R47

current master binary can't decode the testnet genesis file because of above change.

It's part of bigger stream of ongoing refactoring: cosmos/cosmos-sdk#7357

[yihuang]

• investigate if it's possible to do snapshot in tendermint before upgrade, then we don't need to worry about migrating old abci messages.
• then we can focus on migration of abci state storage.
• investigate a potential issue that node paniced too soon, the block is not being relayed successfully.

[tomtau]

this was more relevant to pre-release versions which broke in undocumented ways -- it should be clearer now, but perhaps we can open separate issues for mainnet/testnet once the final things are up and running