Added a debug_backtrace call

test/more/a.php

@@ -6,3 +6,5 @@
 echo '[more/a] file: ' . __FILE__ . ', line: ' . __LINE__ . ', dir: ' . __DIR__ . PHP_EOL;
 require_once 'b.php';
 echo '[more/a] file: ' . __FILE__ . ', line: ' . __LINE__ . ', dir: ' . __DIR__ . PHP_EOL;
+
+var_dump(debug_backtrace());