Test Design and Execution is a key process area at TMMi Level 2, not Level 3. However, other process areas at TMMi Level 3 include Non-functional Testing, Peer Reviews, and Test Lifecycle and Integration. Test Design and Execution plays a foundational role in laying down the practices for creating and executing test cases, especially at earlier maturity levels. By TMMi Level 3, processes become more sophisticated with a broader range of testing techniques and integration into the overall lifecycle.

Reference: 'TMMi level 3 includes process areas such as Non-functional Testing, Test Lifecycle and Integration, and Peer Reviews'.