The other databases have moodle_temptable objects to hold references to temporary tables. The actual class doesn't seem to do much itself, but if it's not present then you get test failures as Moodle tries to call a function on it.

You can pass them into the moodle_database constructor, but I'm not sure where the moodle_database (or rather it's more specific subclasses) get created.

Some of the other databases seem to create this after establishing the connection. But I couldn't quickly get this to work for SQLite.

Need some more understanding of what's going on here.