Q:

How do you test soil for the nutrients present in it? 

I recently noticed that my rose garden has been in a very terrible state.  The roses keep dying.  I tested the soil for its pH and that was fine.  
Now I'm wondering how would I carry out a test to see what specific nutrients I should use to get my soil better. 

A:

Send soil samples to a soil lab (e.g., here).  
They will likely use the Mehlich III extractant   method to extract and quantify the nutrients (most importantly the bases such as  Ca, Mg, K, and Na).  Will cost less than $25. 