Requirement-based test generation (RBTG) is a verification and validation technique, which ensures the conformance of a final product with its requirements. In collaboration with an industry partner, we studied and analyzed their current practice of applying RBTG in the context of developing a family of subsea oil and gas production systems, which are cyber-physical systems. The company aims at improving their current RBTG practice by enhancing the reuse of test artifacts across different products. Due to the complexity of developing such systems and being in the context of system product-line engineering, achieving this goal requires a systematic approach for RBTG. As the first step to this end, we conducted a domain analysis with the industry partner to characterize their current practice of applying RBTG and to identify their needs and challenges. In this paper, we report results of the domain analysis. Moreover, we discuss the limitations of employing existing RBTG approaches in an industrial setting and suggest directions for improvement.