Can I use mysqlslap to test specific databases/tables? Or just the mysqlslap database?
To test a specific database, use the --create-schema option. The options name is a bit misleading, as it does not create the schema if it already exists.
mysqlslap --create-schema=yourdatabase --no-drop --user=myuser -p
CAUTION: If you combine --create-schema with --auto-generate-sql and forget to add --no-drop, the schema is dropped after completion. See official docs for more info.