reverted:
--- b/core/modules/system/src/Tests/Database/TemporaryQueryTest.php
+++ a/core/modules/system/src/Tests/Database/TemporaryQueryTest.php
@@ -31,7 +31,7 @@
     $data = json_decode($this->getRawContent());
     if ($data) {
       $this->assertEqual($this->countTableRows('test'), $data->row_count, 'The temporary table contains the correct amount of rows.');
+      $this->assertFalse(db_table_exists($data->table_name), 'The temporary table is, indeed, temporary.');
-      $this->assertFalse(\Drupal::database()->schema()->tableExists($data->table_name), 'The temporary table is, indeed, temporary.');
     }
     else {
       $this->fail('The creation of the temporary table failed.');
only in patch2:
unchanged:
--- a/core/modules/system/tests/src/Functional/Database/TemporaryQueryTest.php
+++ b/core/modules/system/tests/src/Functional/Database/TemporaryQueryTest.php
@@ -29,7 +29,7 @@ public function testTemporaryQuery() {
     $data = json_decode($this->getSession()->getPage()->getContent());
     if ($data) {
       $this->assertEqual($this->countTableRows('test'), $data->row_count, 'The temporary table contains the correct amount of rows.');
-      $this->assertFalse(db_table_exists($data->table_name), 'The temporary table is, indeed, temporary.');
+      $this->assertFalse(\Drupal::database()->schema()->tableExists($data->table_name), 'The temporary table is, indeed, temporary.');
     }
     else {
       $this->fail('The creation of the temporary table failed.');