--- /dev/null
+<?php
+
+namespace Drupal\views_test_formatter\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Field\Plugin\Field\FieldFormatter\NumericUnformattedFormatter;
+
+/**
+ * Plugin implementation of the 'number_unformatted_with_attachment' formatter.
+ *
+ * @FieldFormatter(
+ * id = "number_unformatted_with_attachment",
+ * label = @Translation("Unformatted, with attachments"),
+ * field_types = {
+ * "integer",
+ * "decimal",
+ * "float"
+ * }
+ * )
+ */
+class AttachmentTestFormatter extends NumericUnformattedFormatter {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function viewElements(FieldItemListInterface $items, $langcode) {
+ $elements = parent::viewElements($items, $langcode);
+
+ // Add dummy attachments.
+ $entity_id = $items->getEntity()->id();
+ $elements['#attached']['library'][] = 'foo/fake_library';
+ $elements['#attached']['drupalSettings']['AttachmentIntegerFormatter'][$entity_id] = $entity_id;
+
+ return $elements;
+ }
+
+}