### Question:
FormController implements FxmlController { protected List<FormFieldController> findInvalidFields() { return subscribedFields.values().stream().filter(not(FormFieldController::isValid)).collect(Collectors.toList()); }  void subscribeToField(FormFieldController formField); void unsubscribeToField(FormFieldController formField); T getField(String formFieldName); abstract void submit();  }### Answer:
@Test public void findingInvalidFieldsReturnsInvalidOnes() { assertThat(formController.findInvalidFields()).containsExactly(INVALID_FIELD); }