setIndexes example

    $entity = $this->container->get('entity_type.manager')
      ->getStorage($entity_type)
      ->create([
        'id' => 1,
        'revision_id' => 1,
      ]);
    $entity->$field_name->value = 'field data';
    $entity->enforceIsNew();
    $entity->save();

    // Add an index.     $field_storage->setIndexes(['value' => [['value', 255]]]);
    $field_storage->save();
    foreach ($tables as $table) {
      $this->assertTrue(Database::getConnection()->schema()->indexExists($table, "{$field_name}_value"), "Index on value created in $table");
    }

    // Add a different index, removing the existing custom one.     $field_storage->setIndexes(['value_format' => [['value', 127], ['format', 127]]]);
    $field_storage->save();
    foreach ($tables as $table) {
      $this->assertTrue(Database::getConnection()->schema()->indexExists($table, "{$field_name}_value_format"), "Index on value_format created in $table");
      $this->assertFalse(Database::getConnection()->schema()->indexExists($table, "{$field_name}_value"), "Index on value removed in $table");
    }