What is testing in CMMI ? CMMI address the quality issues by improving the overall development process. Testing is, in a way "hidden" in the process that is no clear guideline on how to do and achieve good testing goal.
Now there a TMM (Test Maturity Model) to fill the gap. I can across an article "Guidelines for Testing Maturity" by a Dutch QA professional Erik Van Veenendaal. Do a nets search, you would be able to find some very good articles on TMM.