Final answer:
User interface testing would identify flaws in a program's command-line interface.
Step-by-step explanation:
The type of interface testing that would identify flaws in a program's command-line interface is User interface testing. User interface testing focuses on evaluating the interactions between users and a software application, including testing the command-line interface for usability and functionality.
By conducting user interface testing, flaws or issues in the command-line interface can be identified and addressed, ensuring a better user experience.