A Design Test Case developer is responsible for creating detailed, comprehensive, and well-structured test cases. Their role includes understanding the software's functional requirements, designing scenarios that will effectively test these functions, and documenting the expected results. They are also tasked with identifying and defining the necessary test data, setting up the test environment, and sometimes executing the tests. Their work is vital in detecting any bugs or issues in the software, verifying the system's functionality, and ensuring that the final product meets the quality standards and requirements. They often collaborate closely with other team members, like software developers and product managers.