added test code for #65045.

Author: Rui Hirokawa

ext/mbstring/tests/bug65045.phpt

@@ -0,0 +1,29 @@
+--TEST--
+Bug #65045: mb_convert_encoding breaks well-formed character
+--SKIPIF--
+<?php extension_loaded('mbstring') or die('skip mbstring not available'); ?>
+--FILE--
+<?php
+
+//declare(encoding = 'UTF-8');
+mb_internal_encoding('UTF-8');
+
+$str = "\xF0\xA4\xAD".  "\xF0\xA4\xAD\xA2"."\xF0\xA4\xAD\xA2";
+$expected = "\xEF\xBF\xBD"."\xF0\xA4\xAD\xA2"."\xF0\xA4\xAD\xA2";
+
+$str2 = "\xF0\xA4\xAD\xA2"."\xF0\xA4\xAD\xA2"."\xF0\xA4\xAD";
+$expected2 = "\xF0\xA4\xAD\xA2"."\xF0\xA4\xAD\xA2"."\xEF\xBF\xBD";
+
+mb_substitute_character(0xFFFD);
+var_dump(
+    $expected === htmlspecialchars_decode(htmlspecialchars($str, ENT_SUBSTITUTE, 'UTF-8')),
+    $expected2 === htmlspecialchars_decode(htmlspecialchars($str2, ENT_SUBSTITUTE, 'UTF-8')), 
+    $expected === mb_convert_encoding($str, 'UTF-8', 'UTF-8'),
+    $expected2 === mb_convert_encoding($str2, 'UTF-8', 'UTF-8')
+);
+
+--EXPECT--
+bool(true)
+bool(true)
+bool(true)
+bool(true)