src/main/java/models/Course.java

@@ -37,14 +37,15 @@ public class Course {
         return students;
     }
 
-    public void showStudents() {
+    public String getStudentsDisplay() {
         if (students.isEmpty()) {
-            System.out.println("  No students enrolled yet.");
+            return "  No students enrolled yet.";
         } else {
-            System.out.println("  Students in " + name + ":");
+            StringBuilder sb = new StringBuilder("  Students in " + name + ":\n");
             for (Student s : students) {
-                System.out.println("    - " + s.getUsername());
+                sb.append("    - ").append(s.getUsername()).append("\n");
             }
+            return sb.toString();
         }
     }