Logically, the application development cannot start and get tested if you do not have clarity about the requirements. However, you would have to start, considering that the needs are not fixed and will keep changing during the course of development. The two methods you can adopt to test the document without the requirements getting freezed are listed below. Method1 Start working with the requirements you already have and build the product your end user requires. Keep scope and time for the upgrades and changes your client might come up with during the course of the project development. The idea is to consider the document you have as the final one until you get changes from the client. Method2 If it is a request for a software upgrade, you can use the current version as the reference to test and release the upgraded product. Keep your previous interactions with the client in mind and try to infer how often he can change the requirements and how intense they can get. The idea is to use your experience with the client and the product to develop and test the new product under question. These two are simple yet effective methods that test engineers in the current times can use. They need to keep room for change and accept the modified requirements when they come to offer an apt end product to the client.