The top management has feeling that when there are any changes in the technology being used, development schedules etc, it was a waste of time to update the Test Plan. Instead, they were emphasizing that you should put your time into testing than working on the test plan. Your Project Manager asked for your opinion. You have argued that Test Plan is very important and you need to update your test plan from time to time. It’s not a waste of time and testing activities would be more effective when you have your plan clear. Use some metrics. How you would support your argument to have the test plan consistently updated all the time.