--- /dev/null
+<?php
+
+namespace Drupal\Tests\system\Functional\Update;
+
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\FunctionalTests\Update\UpdatePathTestBase;
+
+/**
+ * Tests system_post_update_add_region_to_entity_displays().
+ *
+ * @group Update
+ */
+class UpdateEntityDisplayTest extends UpdatePathTestBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ protected function setDatabaseDumpFiles() {
+ $this->databaseDumpFiles = [
+ __DIR__ . '/../../../../tests/fixtures/update/drupal-8.bare.standard.php.gz',
+ ];
+ }
+
+ /**
+ * Tests that entity displays are updated with regions for their fields.
+ */
+ public function testUpdate() {
+ // No region key appears pre-update.
+ $entity_form_display = EntityFormDisplay::load('node.article.default');
+ $options = $entity_form_display->getComponent('body');
+ $this->assertFalse(array_key_exists('region', $options));
+
+ $entity_view_display = EntityViewDisplay::load('node.article.default');
+ $options = $entity_view_display->getComponent('body');
+ $this->assertFalse(array_key_exists('region', $options));
+
+ $this->runUpdates();
+
+ // The region key has been populated with 'content'.
+ $entity_form_display = EntityFormDisplay::load('node.article.default');
+ $options = $entity_form_display->getComponent('body');
+ $this->assertIdentical('content', $options['region']);
+
+ $entity_view_display = EntityViewDisplay::load('node.article.default');
+ $options = $entity_view_display->getComponent('body');
+ $this->assertIdentical('content', $options['region']);
+ }
+
+}