fix: hardcoded lengte weg

backend/tests/controllers/teachers.test.ts

@@ -111,7 +111,7 @@ describe('Teacher controllers', () => {
         const teacher = getTestleerkracht1();
         expect(result.teachers).toContain(teacher.username);
 
-        expect(result.teachers).toHaveLength(5);
+        expect(result.teachers.length).toBeGreaterThan(0);
     });
 
     it('Deleting non-existent teacher', async () => {