new file mode 100644
--- /dev/null
+++ b/upstream_hash.t
@@ -0,0 +1,225 @@
+#!/usr/bin/perl
+
+# (C) Sergey Kandaurov
+# (C) Nginx, Inc.
+
+# Tests for upstream hash balancer module.
+
+###############################################################################
+
+use warnings;
+use strict;
+
+use Test::More;
+
+BEGIN { use FindBin; chdir($FindBin::Bin); }
+
+use lib 'lib';
+use Test::Nginx;
+
+###############################################################################
+
+select STDERR; $| = 1;
+select STDOUT; $| = 1;
+
+my $t = Test::Nginx->new()->has(qw/http proxy rewrite upstream_hash/);
+
+$t->write_file_expand('nginx.conf', <<'EOF');
+
+%%TEST_GLOBALS%%
+
+daemon off;
+
+events {
+}
+
+http {
+    %%TEST_GLOBALS_HTTP%%
+
+    upstream u {
+        hash $arg_a;
+        server 127.0.0.1:8081;
+        server 127.0.0.1:8082;
+        server 127.0.0.1:8083;
+    }
+
+    upstream u2 {
+        hash $arg_a;
+        server 127.0.0.1:8081;
+        server 127.0.0.1:8083;
+    }
+
+    upstream cw {
+        hash $arg_a consistent;
+        server 127.0.0.1:8081;
+        server 127.0.0.1:8082;
+        server 127.0.0.1:8083 weight=10;
+    }
+
+    upstream cw2 {
+        hash $arg_a consistent;
+        server 127.0.0.1:8081;
+        server 127.0.0.1:8083 weight=10;
+    }
+
+    upstream c {
+        hash $arg_a consistent;
+        server 127.0.0.1:8081;
+        server 127.0.0.1:8082;
+        server 127.0.0.1:8083;
+    }
+
+    upstream c2 {
+        hash $arg_a consistent;
+        server 127.0.0.1:8081;
+        server 127.0.0.1:8083;
+    }
+
+    upstream bad {
+        hash $arg_a;
+        server 127.0.0.1:8081;
+        server 127.0.0.1:8084;
+    }
+
+    upstream cbad {
+        hash $arg_a consistent;
+        server 127.0.0.1:8081;
+        server 127.0.0.1:8084;
+    }
+
+    server {
+        listen       127.0.0.1:8080;
+        server_name  localhost;
+
+        location / {
+            proxy_pass http://u;
+        }
+        location /2 {
+            proxy_pass http://u2;
+        }
+        location /cw {
+            proxy_pass http://cw;
+        }
+        location /cw2 {
+            proxy_pass http://cw2;
+        }
+        location /c {
+            proxy_pass http://c;
+        }
+        location /c2 {
+            proxy_pass http://c2;
+        }
+        location /bad {
+            proxy_pass http://bad;
+        }
+        location /cbad {
+            proxy_pass http://cbad;
+        }
+        location /pnu {
+            proxy_pass http://u/;
+            proxy_next_upstream http_502;
+        }
+    }
+
+    server {
+        listen       127.0.0.1:8081;
+        listen       127.0.0.1:8082;
+        listen       127.0.0.1:8083;
+        server_name  localhost;
+
+        add_header X-Port $server_port;
+
+        location / {
+            return 204;
+        }
+
+        location /502 {
+            if ($server_port = 8083) {
+                return 502;
+            }
+            return 204;
+        }
+    }
+}
+
+EOF
+
+$t->try_run('no upstream hash')->plan(11);
+
+###############################################################################
+
+# Ony requests for absent peer are moved to other peers if hash is consistent.
+# Check this by comparing two upstreams with different number of peers.
+
+ok(!cmp_peers([iter('/', 20)], [iter('/2', 20)], 8082), 'inconsistent');
+ok(cmp_peers([iter('/c', 20)], [iter('/c2', 20)], 8082), 'consistent');
+ok(cmp_peers([iter('/cw', 20)], [iter('/cw2', 20)], 8082), 'consistent weight');
+
+like(many('/?a=1', 10), qr/808\d: 10/, 'stable hash');
+like(many('/c?a=1', 10), qr/808\d: 10/, 'stable hash - consistent');
+
+my @res = iter('/', 10);
+
+is(@res, 10, 'all hashed peers');
+
+@res = grep { $_ != 8083 } @res;
+my @res2 = iter('/502', 10);
+
+is_deeply(\@res, \@res2, 'no proxy_next_upstream');
+isnt(@res2, 10, 'no proxy_next_upstream peers');
+
+is(iter('/pnu/502', 10), 10, 'proxy_next_upstream peers');
+
+@res = grep { $_ == 8081 } iter('/bad', 20);
+is(@res, 20, 'all hashed peers - bad');
+
+@res = grep { $_ == 8081 } iter('/cbad', 20);
+is(@res, 20, 'all hashed peers - bad consistent');
+
+###############################################################################
+
+# Returns true if two arrays follow consistency, i.e., they may only differ
+# by @args present in $p, but absent in $p2, for the same indices.
+
+sub cmp_peers {
+	my ($p, $p2, @args) = @_;
+
+	for my $i (0 .. $#$p) {
+		next if @{$p}[$i] == @{$p2}[$i];
+		next if (grep $_ == @{$p}[$i], @args);
+		return 0;
+	}
+
+	return 1;
+}
+
+# series of requests, each with unique hash key
+
+sub iter {
+	my ($uri, $count) = @_;
+	my @res;
+
+	for my $i (1 .. $count) {
+		if (http_get("$uri/?a=$i") =~ /X-Port: (\d+)/) {
+			push @res, $1 if defined $1;
+		}
+	}
+
+	return @res;
+}
+
+sub many {
+	my ($uri, $count) = @_;
+	my %ports;
+
+	for my $i (1 .. $count) {
+		if (http_get($uri) =~ /X-Port: (\d+)/) {
+			$ports{$1} = 0 unless defined $ports{$1};
+			$ports{$1}++;
+		}
+	}
+
+	return join ', ', map { $_ . ": " . $ports{$_} } sort keys %ports;
+}
+
+###############################################################################