Just checking connectivity is a very risky strategy. I would recommend a more thorough test, which would include transformation and the actual application. Testing every application might not be possible, but you should be able to pick a few key ones that the business uses and run through them, identify some key indicator (for example total sales, stock count, etc) that can provide you with a good feel of the data in the application, reload on the new database and verify that the numbers still matches.
agreed and that is why I recommended to check if the extractions scripts work, because normally in the transformations your qvd's are already loaded and there is no need to go back into the DB to pull any data
