integrationtests: fix proxy test on Windows (#4023)

integrationtests/tools/proxy/proxy_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"net"
+	"runtime"
 	"runtime/pprof"
 	"strconv"
 	"strings"
@@ -68,7 +69,11 @@ var _ = Describe("QUIC Proxy", func() {
 			addr, err := net.ResolveUDPAddr("udp", "localhost:"+strconv.Itoa(proxy.LocalPort()))
 			Expect(err).ToNot(HaveOccurred())
 			_, err = net.ListenUDP("udp", addr)
+			if runtime.GOOS == "windows" {
+				Expect(err).To(MatchError(fmt.Sprintf("listen udp 127.0.0.1:%d: bind: Only one usage of each socket address (protocol/network address/port) is normally permitted.", proxy.LocalPort())))
+			} else {
 				Expect(err).To(MatchError(fmt.Sprintf("listen udp 127.0.0.1:%d: bind: address already in use", proxy.LocalPort())))
+			}
 			Expect(proxy.Close()).To(Succeed()) // stopping is tested in the next test
 		})