The Structured Data on Commons (SDC) project will change the setup of Commons considerably. Most importantly, Commons will be the only wiki in the wmf cluster running the WikibaseMediaInfo extension, and it will be the only wiki that is a Wikibase repo and also a client to another Wikibase repo.
* Domain: test-commons.wikimedia.org
* Database: testcommonswiki
* Config: as similar to commonswiki as possible; should be set to $wgMultiContentRevisionSchemaMigrationStage = SCHEMA_COMPAT_WRITE_BOTH | SCHEMA_COMPAT_READ_OLD right away.
Having a test-commons.wikimedia.org in deployment group 0 on the live cluster will allow us to do two things:
# try out the new configuration, before deploying it to commons. This also includes testing the MCR schema migration, before enabling the extension.
# later, once SDC is deployed on commons, having test-commons.wikimedia.org will ensure that weekly deployments won't break the unique setup on commons.