diff -u b/core/modules/text/tests/src/Kernel/TextWithSummaryItemTest.php b/core/modules/text/tests/src/Kernel/TextWithSummaryItemTest.php
--- b/core/modules/text/tests/src/Kernel/TextWithSummaryItemTest.php
+++ b/core/modules/text/tests/src/Kernel/TextWithSummaryItemTest.php
@@ -71,15 +71,6 @@
     $entity->name->value = $this->randomMachineName();
     $entity->save();
 
-    // Test constraint failure.
-    $entity_fail = $storage->create();
-    $entity_fail->summary_field->value = $this->randomMachineName();
-    $entity_fail->summary_field->summary = $this->randomMachineName();
-    $entity_fail->summary_field->format = 'failure_format';
-    $entity_fail->name->value = $this->randomMachineName();
-    $violations = $entity_fail->validate();
-    $this->assertCount(2, $violations);
-
     $entity = $storage->load($entity->id());
     $this->assertInstanceOf(FieldItemListInterface::class, $entity->summary_field);
     $this->assertInstanceOf(FieldItemInterface::class, $entity->summary_field[0]);
reverted:
--- b/core/modules/text/text.install
+++ /dev/null
@@ -1,31 +0,0 @@
-<?php
-
-/**
- * @file
- * Install, update, and uninstall functions for the text module.
- */
-
-use Drupal\text\Plugin\Field\FieldType\TextItemBase;
-use Drupal\Core\Config\Entity\ConfigEntityUpdater;
-use Drupal\field\FieldConfigInterface;
-
-/**
- * Add allowed_formats setting to existing text fields.
- */
-function text_update_10101(&$sandbox) {
-  \Drupal::classResolver(ConfigEntityUpdater::class)
-    ->update($sandbox, 'field_config', function (FieldConfigInterface $field_config) {
-      $class = get_class($field_config);
-      // Deal only with text fields and descendants.
-      if ($class == TextItemBase::class || is_subclass_of($class, TextItemBase::class)) {
-        // Get the existing allowed_formats setting.
-        $allowed_formats = $field_config->get('settings.allowed_formats');
-        if (!is_array($allowed_formats) && empty($allowed_formats)) {
-          // Save default value if existing value not present.
-          $field_config->set('settings.allowed_formats', []);
-        }
-        return TRUE;
-      }
-      return FALSE;
-    });
-}
only in patch2:
unchanged:
--- a/core/modules/text/text.post_update.php
+++ b/core/modules/text/text.post_update.php
@@ -8,6 +8,8 @@
 use Drupal\Core\Config\Entity\ConfigEntityUpdater;
 use Drupal\Core\Entity\Display\EntityDisplayInterface;
 use Drupal\text\Plugin\Field\FieldWidget\TextareaWithSummaryWidget;
+use Drupal\text\Plugin\Field\FieldType\TextItemBase;
+use Drupal\field\FieldConfigInterface;
 
 /**
  * Implements hook_removed_post_updates().
@@ -46,3 +48,24 @@ function text_post_update_add_required_summary_flag_form_display(&$sandbox = NUL
 
   $config_entity_updater->update($sandbox, 'entity_form_display', $widget_callback);
 }
+
+/**
+ * Add allowed_formats setting to existing text fields.
+ */
+function test_post_update_allowed_formats(&$sandbox = NULL) {
+  \Drupal::classResolver(ConfigEntityUpdater::class)
+    ->update($sandbox, 'field_config', function (FieldConfigInterface $field_config) {
+      $class = get_class($field_config);
+      // Deal only with text fields and descendants.
+      if ($class == TextItemBase::class || is_subclass_of($class, TextItemBase::class)) {
+        // Get the existing allowed_formats setting.
+        $allowed_formats = $field_config->get('settings.allowed_formats');
+        if (!is_array($allowed_formats) && empty($allowed_formats)) {
+          // Save default value if existing value not present.
+          $field_config->set('settings.allowed_formats', []);
+        }
+        return TRUE;
+      }
+      return FALSE;
+    });
+}