ComputedTestCacheableStringItem.php

<?php

namespace Drupal\entity_test\Plugin\Field\FieldType;

use Drupal\Core\Field\Attribute\FieldType;
use Drupal\Core\Field\FieldStorageDefinitionInterface;
use Drupal\Core\Field\Plugin\Field\FieldType\StringItem;
use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\TypedData\DataDefinition;

/**
 * Defines the 'string' entity field type with cacheability metadata.
 */
class ComputedTestCacheableStringItem extends StringItem {
    
    /**
     * {@inheritdoc}
     */
    public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
        $properties['value'] = DataDefinition::create('computed_test_cacheable_string')->setLabel(new TranslatableMarkup('Text value'))
            ->setSetting('case_sensitive', $field_definition->getSetting('case_sensitive'))
            ->setRequired(TRUE);
        return $properties;
    }

}