The process should be iterative, not sequential

Describing iterative processes in writing is challenging. My explanation may have given you the impression that this process is fully sequential and that you move to the next step only when you have completed the previous one. However, the entire process is meant to be iterative. In practice, I go back and forth between the different steps. Often, when I’m writing test cases, I notice that I missed a partition or boundary, and I go back and improve my test suite.