A wikibase repo per default also has the client code enabled. This is also true for Wikidata. So our CI setup should test that configuration.
This means having three test sets: repo+client, repo only, and client only. Each of them could potentially be tested against sqlight and mysql, and against hhvm and php/zend.
We should at least test repo+client and client-only on mysql+hhv, since these are the configurations we are running on the live sites. For repo only, perhaps testing against sqlite is enough.