Issue #2672888 by fago: BrowserTestBase fails when the webserver runs as another user

core/modules/simpletest/src/TestBase.php

@@ -1532,7 +1532,11 @@ public static function generatePermutations($parameters) {
    * need to get deleted too.
    */
   public static function filePreDeleteCallback($path) {
-    chmod($path, 0700);
+    // When the webserver runs with the same system user as the test runner, we
+    // can make read-only files writable again. If not, chmod will fail while
+    // the file deletion still works if file permissions have been configured
+    // correctly. Thus, we ignore any problems while running chmod.
+    @chmod($path, 0700);
   }
 
   /**

core/tests/Drupal/Tests/BrowserTestBase.php

@@ -557,10 +557,11 @@ protected function setUp() {
    *   The file path.
    */
   public static function filePreDeleteCallback($path) {
-    $success = @chmod($path, 0700);
-    if (!$success) {
-      trigger_error("Can not make $path writable whilst cleaning up test directory. The webserver and phpunit are probably not being run by the same user.");
-    }
+    // When the webserver runs with the same system user as phpunit, we can
+    // make read-only files writable again. If not, chmod will fail while the
+    // file deletion still works if file permissions have been configured
+    // correctly. Thus, we ignore any problems while running chmod.
+    @chmod($path, 0700);
   }
 
   /**