new file mode 100644
--- /dev/null
+++ b/sub_filter.t
@@ -0,0 +1,127 @@
+#!/usr/bin/perl
+
+# (C) Maxim Dounin
+
+# Tests for sub filter.
+
+###############################################################################
+
+use warnings;
+use strict;
+
+use Test::More;
+
+use Socket qw/ CRLF /;
+
+BEGIN { use FindBin; chdir($FindBin::Bin); }
+
+use lib 'lib';
+use Test::Nginx;
+
+###############################################################################
+
+select STDERR; $| = 1;
+select STDOUT; $| = 1;
+
+my $t = Test::Nginx->new()->has(qw/http rewrite sub/)->plan(14)
+	->write_file_expand('nginx.conf', <<'EOF');
+
+%%TEST_GLOBALS%%
+
+daemon off;
+
+events {
+}
+
+http {
+    %%TEST_GLOBALS_HTTP%%
+
+    server {
+        listen       127.0.0.1:8080;
+        server_name  localhost;
+
+        sub_filter_types *;
+        sub_filter foo bar;
+
+        location / {
+        }
+
+        location /once {
+            return 200 $arg_b;
+        }
+
+        location /many {
+            sub_filter_once off;
+            return 200 $arg_b;
+        }
+
+        location /complex {
+            sub_filter abac _replaced;
+            return 200 $arg_b;
+        }
+
+        location /complex2 {
+            sub_filter ababX _replaced;
+            return 200 $arg_b;
+        }
+
+        location /complex3 {
+            sub_filter aab _replaced;
+            return 200 $arg_b;
+        }
+    }
+}
+
+EOF
+
+$t->write_file('foo.html', 'foo');
+$t->write_file('foofoo.html', 'foofoo');
+$t->run();
+
+###############################################################################
+
+like(http_get('/foo.html'), qr/bar/, 'sub_filter');
+like(http_get('/foofoo.html'), qr/barfoo/, 'once default');
+
+like(http_get('/once?b=foofoo'), qr/barfoo/, 'once');
+like(http_get('/many?b=foofoo'), qr/barbar/, 'many');
+
+TODO: {
+local $TODO = 'not yet';
+
+like(http_get('/many?b=fo'), qr/fo/, 'incomplete');
+like(http_get('/many?b=foofo'), qr/barfo/, 'incomplete long');
+
+}
+
+like(http_get('/complex?b=abac'), qr/_replaced/, 'complex');
+like(http_get('/complex?b=abaabac'), qr/aba_replaced/, 'complex 1st char');
+
+TODO: {
+local $TODO = 'not yet';
+
+like(http_get('/complex?b=ababac'), qr/replaced/, 'complex 2nd char');
+
+}
+
+like(http_get('/complex2?b=ababX'), qr/_replaced/, 'complex2');
+
+TODO: {
+local $TODO = 'not yet';
+
+like(http_get('/complex2?b=abababX'), qr/ab_replaced/, 'complex2 long');
+
+}
+
+like(http_get('/complex3?b=aab'), qr/_replaced/, 'complex3 aab in aab');
+
+TODO: {
+local $TODO = 'not yet';
+
+like(http_get('/complex3?b=aaab'), qr/a_replaced/, 'complex3 aab in aaab');
+
+}
+
+like(http_get('/complex3?b=aaaab'), qr/aa_replaced/, 'complex3 aab in aaaab');
+
+###############################################################################