Should this use the preV1Keychains values we just read instead of hardcoding 6u and 0u here? I think that would make the test cover the migration path more directly (read old metadata, apply indices to new v3 wallet, then persist/reload + check that next external/internal addresses are 7 and 1).

Yes absolutely, that's an oversight for sure (hardcoding the correct answer into my test 😆)

Yep this covers the hardcoded part. Should we also persist and then reload from newV3DB before checking the next addresses? I think that would make this prove the migrated v3 persistence state too instead of only the live wallet after calling revealAddressesTo

Makes sense. I applied this with the following:

val wallet = Wallet(
    descriptor = descriptor,
    changeDescriptor = changeDescriptor,
    network = Network.REGTEST,
    persister = newV3DB,
)

wallet.revealAddressesTo(KeychainKind.EXTERNAL, externalPreV1Keychain.lastDerivationIndex)
wallet.revealAddressesTo(KeychainKind.INTERNAL, internalPreV1Keychain.lastDerivationIndex)
wallet.persist(newV3DB)

val reloadedWallet = Wallet.load(
    descriptor = descriptor,
    changeDescriptor = changeDescriptor,
    persister = newV3DB,
)

val addressInfo: AddressInfo = reloadedWallet.revealNextAddress(KeychainKind.EXTERNAL)
val changeAddressInfo: AddressInfo = reloadedWallet.revealNextAddress(KeychainKind.INTERNAL)

assertEquals(addressInfo.index, 7u)
assertEquals(changeAddressInfo.index, 1u)

Could we make sure this test starts from a clean new_v3_wallet.sqlite3 database before creating the persister? Wallet(...) creates a new persisted wallet, and upstream returns DataAlreadyExists if the persister already contains wallet data, so repeated runs on the same app data can fail here before testing the migration path.

Wow good catch. I didn't realize but on local tests reusing an old database already there could definitely be an issue. Fixed now with the following:

// This ensures local tests always create a new DB and don't reuse an old one leftover from prior tests
if (newV3DBFilePath.exists()) newV3DBFilePath.delete()