EntityTestViewsData.php

<?php

namespace Drupal\entity_test;

use Drupal\Component\Utility\NestedArray;
use Drupal\views\EntityViewsData;

/**
 * Provides a view to override views data for test entity types.
 */
class EntityTestViewsData extends EntityViewsData {
    
    /**
     * {@inheritdoc}
     */
    public function getViewsData() {
        $views_data = parent::getViewsData();
        if ($this->entityType
            ->id() === 'entity_test_computed_field') {
            $views_data['entity_test_computed_field']['computed_string_field'] = [
                'title' => $this->t('Computed String Field'),
                'field' => [
                    'id' => 'field',
                    'default_formatter' => 'string',
                    'field_name' => 'computed_string_field',
                ],
            ];
        }
        if ($this->entityType
            ->id() != 'entity_test') {
            return $views_data;
        }
        $views_data = NestedArray::mergeDeep($views_data, \Drupal::state()->get('entity_test.views_data', []));
        return $views_data;
    }

}