quic: skip tests which depend on unimplemented UDP functions on Plan 9

The ReadMsgUDP and WriteMsgUDP methods of UDPConn are not implemented
(yet?) on Plan 9. Skip tests which require them.

Fixes golang/go#68288

Change-Id: Ic6c81b19322d589c10b16da61e9b89284294be05
Reviewed-on: https://go-review.googlesource.com/c/net/+/596795
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>

quic/endpoint_test.go

@@ -13,6 +13,7 @@ import (
 	"io"
 	"log/slog"
 	"net/netip"
+	"runtime"
 	"testing"
 	"time"
 
@@ -69,6 +70,10 @@ func TestStreamTransfer(t *testing.T) {
 }
 
 func newLocalConnPair(t testing.TB, conf1, conf2 *Config) (clientConn, serverConn *Conn) {
+	switch runtime.GOOS {
+	case "plan9":
+		t.Skipf("ReadMsgUDP not supported on %s", runtime.GOOS)
+	}
 	t.Helper()
 	ctx := context.Background()
 	e1 := newLocalEndpoint(t, serverSide, conf1)

quic/udp_test.go

@@ -129,6 +129,8 @@ func runUDPTest(t *testing.T, f func(t *testing.T, u udpTest)) {
 				if test.srcNet == "udp6" && test.dstNet == "udp" {
 					t.Skipf("%v: no support for mapping IPv4 address to IPv6", runtime.GOOS)
 				}
+			case "plan9":
+				t.Skipf("ReadMsgUDP not supported on %s", runtime.GOOS)
 			}
 			if runtime.GOARCH == "wasm" && test.srcNet == "udp6" {
 				t.Skipf("%v: IPv6 tests fail when using wasm fake net", runtime.GOARCH)