After you have changed and tested your code, you consider each requirement that traced to the impacted code. Do you need to change the requirement? Adjust as required. If you change a requirement, you must review the tests and adjust as required. If you feel a need to change the test in order to cover the new code, but you have not changed the requirement, check carefully again. This is certainly possible (if the new code covers a corner case that the requirement does not and should not cover) but should not be common.