fix: gefaalde testen voor class controller gefixt

backend/src/data/users/student-repository.ts

@@ -1,3 +1,4 @@
+import { Class } from '../../entities/classes/class.entity.js';
 import { Student } from '../../entities/users/student.entity.js';
 import { User } from '../../entities/users/user.entity.js';
 import { DwengoEntityRepository } from '../dwengo-entity-repository.js';
@@ -9,6 +10,9 @@ export class StudentRepository extends DwengoEntityRepository<Student> {
     public findByUsername(username: string): Promise<Student | null> {
         return this.findOne({ username: username });
     }
+    public findByClass(cls: Class): Promise<Student[]> {
+        return this.find({ classes: cls });
+    }
     public deleteByUsername(username: string): Promise<void> {
         return this.deleteWhere({ username: username });
     }