reverted:
--- b/core/modules/file/src/Tests/FileManagedFileElementTest.php
+++ a/core/modules/file/src/Tests/FileManagedFileElementTest.php
@@ -6,9 +6,6 @@
  */
 
 namespace Drupal\file\Tests;
-use Drupal\Component\Utility\Bytes;
-use Drupal\Component\Utility\SafeMarkup;
-use Drupal\file\Entity\File;
 
 /**
  * Tests the 'managed_file' element type.
@@ -18,18 +15,6 @@
  *   that aren't related to fields into it.
  */
 class FileManagedFileElementTest extends FileFieldTestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-
-    // Setup the max filesize to be the same as the post max size, so we can
-    // post a file which let's PHP to exceed its post max size.
-    ini_set('upload_max_filesize', ini_get('post_max_size'));
-  }
-
   /**
    * Tests the managed_file element type.
    */
@@ -121,28 +106,6 @@
 
             $this->drupalPostForm(NULL, array(), t('Save'));
             $this->assertRaw(t('The file ids are %fids.', array('%fids' => '')), 'Submission after file upload and removal was successful.');
-
-            // Upload a file which exceeds the configured post_max_size limit.
-            $post_max_size_ini = ini_get('post_max_size');
-            if ($post_max_size_ini) {
-              $post_max_size = Bytes::toInt($post_max_size_ini);
-              $big_test_data = str_repeat('a', $post_max_size * 1.1);
-              file_put_contents('public://test.dat', $big_test_data);
-
-              /** @var \Drupal\Core\File\FileSystemInterface $file_system */
-              $file_system = \Drupal::service('file_system');
-              $edit = array($file_field_name => $file_system->realpath('public://test.dat'));
-              if ($ajax) {
-                $this->drupalPostAjaxForm(NULL, $edit, $input_base_name . '_upload_button');
-                $this->assertText(SafeMarkup::format('An unrecoverable error occurred. The uploaded file likely exceeded the maximum file size (@post_max_size) that this server supports.', ['@post_max_size' => format_size(file_upload_max_size())]));
-              }
-              else {
-                // @todo Currently the post request just fails, as there is no
-                //   input, so I guess we can't protect against it? This would
-                //   be odd.
-                $this->drupalPostForm(NULL, $edit, t('Upload'));
-              }
-            }
           }
         }
       }