trait EntityReferenceTestTrait

trait EntityReferenceTestTrait {
    
    /**
     * Creates a field of an entity reference field storage on the specified bundle.
     *
     * @param string $entity_type
     *   The type of entity the field will be attached to.
     * @param string $bundle
     *   The bundle name of the entity the field will be attached to.
     * @param string $field_name
     *   The name of the field; if it already exists, a new instance of the existing
     *   field will be created.
     * @param string $field_label
     *   The label of the field.
     * @param string $target_entity_type
     *   The type of the referenced entity.
     * @param string $selection_handler
     *   The selection handler used by this field.
     * @param array $selection_handler_settings
     *   An array of settings supported by the selection handler specified above.
     *   (e.g. 'target_bundles', 'sort', 'auto_create', etc).
     * @param int $cardinality
     *   The cardinality of the field.
     *
     * @see \Drupal\Core\Entity\Plugin\EntityReferenceSelection\SelectionBase::buildConfigurationForm()
     */
    protected function createEntityReferenceField($entity_type, $bundle, $field_name, $field_label, $target_entity_type, $selection_handler = 'default', $selection_handler_settings = [], $cardinality = 1) {
        // Look for or add the specified field to the requested entity bundle.
        if (!FieldStorageConfig::loadByName($entity_type, $field_name)) {
            FieldStorageConfig::create([
                'field_name' => $field_name,
                'type' => 'entity_reference',
                'entity_type' => $entity_type,
                'cardinality' => $cardinality,
                'settings' => [
                    'target_type' => $target_entity_type,
                ],
            ])->save();
        }
        if (!FieldConfig::loadByName($entity_type, $bundle, $field_name)) {
            FieldConfig::create([
                'field_name' => $field_name,
                'entity_type' => $entity_type,
                'bundle' => $bundle,
                'label' => $field_label,
                'settings' => [
                    'handler' => $selection_handler,
                    'handler_settings' => $selection_handler_settings,
                ],
            ])->save();
        }
    }

}