new file mode 100644
--- /dev/null
+++ b/quic_key_update.t
@@ -0,0 +1,99 @@
+#!/usr/bin/perl
+
+# (C) Sergey Kandaurov
+# (C) Nginx, Inc.
+
+# Tests for QUIC key update.
+
+###############################################################################
+
+use warnings;
+use strict;
+
+use Test::More;
+
+BEGIN { use FindBin; chdir($FindBin::Bin); }
+
+use lib 'lib';
+use Test::Nginx;
+use Test::Nginx::HTTP3;
+
+###############################################################################
+
+select STDERR; $| = 1;
+select STDOUT; $| = 1;
+
+my $t = Test::Nginx->new()->has(qw/http http_v3 cryptx/)
+	->has_daemon('openssl')->plan(3);
+
+$t->write_file_expand('nginx.conf', <<'EOF');
+
+%%TEST_GLOBALS%%
+
+daemon off;
+
+events {
+}
+
+http {
+    %%TEST_GLOBALS_HTTP%%
+
+    ssl_certificate_key localhost.key;
+    ssl_certificate localhost.crt;
+
+    server {
+        listen       127.0.0.1:%%PORT_8980_UDP%% quic;
+        server_name  localhost;
+
+        location / { }
+    }
+}
+
+EOF
+
+$t->write_file('openssl.conf', <<EOF);
+[ req ]
+default_bits = 2048
+encrypt_key = no
+distinguished_name = req_distinguished_name
+[ req_distinguished_name ]
+EOF
+
+my $d = $t->testdir();
+
+foreach my $name ('localhost') {
+	system('openssl req -x509 -new '
+		. "-config $d/openssl.conf -subj /CN=$name/ "
+		. "-out $d/$name.crt -keyout $d/$name.key "
+		. ">>$d/openssl.out 2>&1") == 0
+		or die "Can't create certificate for $name: $!\n";
+}
+
+$t->run();
+
+###############################################################################
+
+my ($s, $sid, $frames, $frame);
+
+$s = Test::Nginx::HTTP3->new();
+ok(get($s), 'request');
+
+# sets the Key Phase bit
+
+$s->key_update();
+ok(get($s), 'key update 1');
+
+# clears the Key Phase bit
+
+$s->key_update();
+ok(get($s), 'key update 2');
+
+###############################################################################
+
+sub get {
+	my ($s) = @_;
+	my $frames = $s->read(all => [{ sid => $s->new_stream(), fin => 1 }]);
+	grep { $_->{type} eq "HEADERS" } @$frames;
+}
+
+###############################################################################