I am migrating a legacy system from Oracle Form to Web Application. The migration is conducted with code study and interview.
As the requirement is to migrate the existing system to Web application and keep all existing functionalities.
There are some differences in behavior between Web application and exiting system because of completely different architecture. In addition, the functionalities of existing system is not well known.
In this situation, how should I prepare test case in order to ensure the quality of the system and also meet the requirements of the project?
Edit: I would like to mention that this project use Agile Methodology.
Similar Question: Writing tests for code whose purpose I don't understand
Difference: The Tester of "Writing tests for code whose purpose I don't understand" well know the input and output of the System. But in this situation, testers does not know the input and output of the System and also the functionalities of the System.