Set version to 0.22.7 in src/CMakeLists.txt, run the node on an already synced folder and verify that it fails with `ERROR: LoadBlockIndexGuts: Invalid block index database version: 250300`
This failure is caused by `CBlockTreeDB::Upgrade` not upgrading the version in the database, since it is already larger than 0.22.7, and then `CBlockTreeDB::LoadBlockIndexGuts` failing to load a database with a version number different than the node version.
Restart a new IBD from scratch (`mv ~/.bitcoin/testnet3/ ~/.bitcoin/testnet3_bck`), wait a few minutes to have a few blocks and a block index. Then bump the version number, rerun cmake, recompile, restart the node, and check that it fails to start and tells you to reindex with the following message:
```
2022-04-25T08:52:14Z
The database is too old. The block index cannot be upgraded and reindexing is required.
2022-04-25T08:52:14Z : Error upgrading block index database.
Please restart with -reindex or -reindex-chainstate to recover.
: Error upgrading block index database.
Please restart with -reindex or -reindex-chainstate to recover.
2022-04-25T08:52:14Z Aborted block database rebuild. Exiting.
```