Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

vendor/symfony/debug/Resources/ext/tests/002_1.phpt

@@ -0,0 +1,47 @@
+--TEST--
+Test symfony_debug_backtrace in case of non fatal error
+--SKIPIF--
+<?php if (!extension_loaded("symfony_debug")) print "skip"; ?>
+--FILE--
+<?php
+
+function bar()
+{
+    bt();
+}
+
+function bt()
+{
+    print_r(symfony_debug_backtrace());
+
+}
+
+bar();
+
+?>
+--EXPECTF--
+Array
+(
+    [0] => Array
+        (
+            [file] => %s
+            [line] => %d
+            [function] => bt
+            [args] => Array
+                (
+                )
+
+        )
+
+    [1] => Array
+        (
+            [file] => %s
+            [line] => %d
+            [function] => bar
+            [args] => Array
+                (
+                )
+
+        )
+
+)