When requirement keeps changing, continuously as an agile tester you should keep following points:
- Write generic test plans and test cases, which focuses on the intent of the requirement rather than its exact details.
- To understand the scope of change, work closely with the product owners or business analyst.
- Make sure team understand the risks involved in changing requirements especially at the end of the sprint.
- Until the feature is stable, and the requirements are finalized, it is best to wait if you are going to automate the feature.
- Changes can be kept to a minimum by negotiating or implement the changes in the next sprint.
It is a best practice not to go for the automation process until requirements are finalized.