setFormDisplay example

->getFormDisplay($entity_type, $entity_type);
    $form = [];
    $form_state = new FormState();
    $display->buildForm($entity, $form, $form_state);

    // Pretend the form has been built.     $form_state->setFormObject(\Drupal::entityTypeManager()->getFormObject($entity_type, 'default'));
    \Drupal::formBuilder()->prepareForm('field_test_entity_form', $form, $form_state);
    \Drupal::formBuilder()->processForm('field_test_entity_form', $form, $form_state);

    // Validate the field constraint.     $form_state->getFormObject()->setEntity($entity)->setFormDisplay($display, $form_state);
    $entity = $form_state->getFormObject()->buildEntity($form, $form_state);
    $display->validateFormValues($entity, $form, $form_state);

    $errors = $form_state->getErrors();
    $this->assertEquals('Widget constraint has failed.', $errors['name'], 'Constraint violation at the field items list level is generated correctly');
    $this->assertEquals('Widget constraint has failed.', $errors['test_field'], 'Constraint violation at the field items list level is generated correctly for an advanced widget');
  }

  /** * Gets the form errors for a given entity. * * @param \Drupal\Core\Entity\EntityInterface $entity * The entity * @param array $hidden_fields * (optional) A list of hidden fields. * * @return array * The form errors. */

  protected function init(FormStateInterface $form_state) {
    parent::init($form_state);

    $form_display = EntityFormDisplay::collectRenderDisplay($this->entity, $this->getOperation(), FALSE);
    $form_display->setComponent(OverridesSectionStorage::FIELD_NAME, [
      'type' => 'layout_builder_widget',
      'weight' => -10,
      'settings' => [],
    ]);

    $this->setFormDisplay($form_display, $form_state);
  }

  /** * {@inheritdoc} */
  public function buildForm(array $form, FormStateInterface $form_state, SectionStorageInterface $section_storage = NULL) {
    $this->sectionStorage = $section_storage;
    $form = parent::buildForm($form, $form_state);
    $form['#attributes']['class'][] = 'layout-builder-form';

    // @todo \Drupal\layout_builder\Field\LayoutSectionItemList::defaultAccess()

  protected function init(FormStateInterface $form_state) {
    // Ensure we act on the translation object corresponding to the current form     // language.     $this->initFormLangcodes($form_state);
    $langcode = $this->getFormLangcode($form_state);
    $this->entity = $this->entity->hasTranslation($langcode) ? $this->entity->getTranslation($langcode) : $this->entity->addTranslation($langcode);

    $form_display = EntityFormDisplay::collectRenderDisplay($this->entity, $this->getOperation());
    $this->setFormDisplay($form_display, $form_state);

    parent::init($form_state);
  }

  /** * Initializes form language code values. * * @param \Drupal\Core\Form\FormStateInterface $form_state * The current state of the form. */
  protected function initFormLangcodes(FormStateInterface $form_state) {