What if requirements are changing continuously?
Changes to requirements are inevitable during the development process, but if the requirements are changing continuously due to some reasons then you have to work in parallel with the management to see how exactly the requirements are changing and make necessary changes in test plans or test strategies early, if any. Requirement changes involves cost, both in terms of money and time, make sure management and customer are well aware of this. Coding is done in a manner (well commented etc.) so as to minimize maintenance and make future changes easy. Use rapid prototyping. Try minimizing requirement changes or postpone them till release 2. etc
Also See:
Requirement Traceability Matrix & Templates