Mobile application development using Flutter/Dart is gaining increasing importance in industries. However, most university curricula lack structured education on these technologies. To address this gap, we have been developing the Flutter Programming Learning Assistant System (FPLAS). It provides code modification problems (CMPs), which are run in a Docker-based environment, where answer validation relies on user interface (UI) image comparisons using ORB and SIFT. In this study, we present an enhanced automated answer-validation method integrating Flutter’s native widget testing framework into FPLAS. This approach tests student answers with test cases that verify widget structures, UI properties, and functional outcomes. Combining widget-level checks with image-based comparisons can further strengthen reliability for visually oriented tasks. This study investigates how the widget testing strengthens feedback quality and enhances the effectiveness of mobile UI programming education.