only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/src/Tests/Table/d6/System.php
+++ b/core/modules/migrate_drupal/src/Tests/Table/d6/System.php
@@ -26,7 +26,9 @@ public function load() {
       ),
       'fields' => array(
         'filename' => array(
-          'type' => 'varchar',
+          // In order to work around the InnoDB 191 character limit on utf8mb4
+          // unique constraints, we set the character set for the field to ASCII.
+          'type' => 'varchar_ascii',
           'not null' => TRUE,
           'length' => '255',
           'default' => '',
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/database_test/database_test.install
+++ b/core/modules/system/tests/modules/database_test/database_test.install
@@ -24,7 +24,9 @@ function database_test_schema() {
       ),
       'name' => array(
         'description' => "A person's name",
-        'type' => 'varchar',
+        // In order to work around the InnoDB 191 character limit on utf8mb4
+        // unique constraints, we set the character set for the field to ASCII.
+        'type' => 'varchar_ascii',
         'length' => 255,
         'not null' => TRUE,
         'default' => '',
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/entity_test/src/Entity/EntityTestStringId.php
+++ b/core/modules/system/tests/modules/entity_test/src/Entity/EntityTestStringId.php
@@ -45,7 +45,10 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
     $fields['id'] = BaseFieldDefinition::create('string')
       ->setLabel(t('ID'))
       ->setDescription(t('The ID of the test entity.'))
-      ->setReadOnly(TRUE);
+      ->setReadOnly(TRUE)
+      // In order to work around the InnoDB 191 character limit on utf8mb4
+      // primary keys, we set the character set for the field to ASCII.
+      ->setSetting('is_ascii', TRUE);
     return $fields;
   }
 
only in patch2:
unchanged:
--- a/core/modules/views/src/Tests/ViewTestData.php
+++ b/core/modules/views/src/Tests/ViewTestData.php
@@ -75,7 +75,9 @@ public static function schemaDefinition() {
         ),
         'name' => array(
           'description' => "A person's name",
-          'type' => 'varchar',
+          // In order to work around the InnoDB 191 character limit on utf8mb4
+          // unique constraints, we set the character set for the field to ASCII.
+          'type' => 'varchar_ascii',
           'length' => 255,
           'not null' => TRUE,
           'default' => '',