Add test case for same strings

Author: youkidearitai

ext/mbstring/tests/mb_trim.phpt

@@ -56,6 +56,9 @@ var_dump(bin2hex(mb_ltrim(mb_convert_encoding("\u{FEFF}漢字", "UTF-16BE", "UTF
 echo "== SJIS ==\n";
 var_dump(mb_convert_encoding(mb_trim("\x81\x40\x82\xa0\x81\x40", "\x81\x40", "SJIS"), "UTF-8", "SJIS"));
 
+echo "== Same strings ==\n";
+var_dump(mb_trim("foo", "oo"));
+
 echo "== \$encoding throws ValueError ==\n";
 try {
     var_dump(mb_trim( "\u{180F}", "", "NULL"));
@@ -107,5 +110,7 @@ string(8) "226f575b"
 string(8) "6f225b57"
 == SJIS ==
 string(3) "あ"
+== Same strings ==
+string(1) "f"
 == $encoding throws ValueError ==
 string(73) "mb_trim(): Argument #3 ($encoding) must be a valid encoding, "NULL" given"