When testing an MVVM setup (ViewModel, Repository, Data provider thingy), would it make sense to, in each of those things, validate that the Response object has the correct data in it, or just to make sure that it's getting the correct object?

In my opinion, it relies on the testing level you want to apply to. for me it needs to have a unit test to make sure that app is receiving the correct data an another integration one to validate the data transformation througth all layers.