net/http: add a test for starting a server with no HTTP/2 and no TLS config

Test for the fix in CL 758560.

Change-Id: I34edf9f14dc5d6a569f20aa3d55d9d136a6a6964
Reviewed-on: https://go-review.googlesource.com/c/go/+/758661
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Nicholas Husin <nsh@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Nicholas Husin <husin@google.com>

src/net/http/serve_test.go

diff --git a/src/net/http/serve_test.go b/src/net/http/serve_test.go
index b2cf43c..f2ba870 100644
--- a/src/net/http/serve_test.go
+++ b/src/net/http/serve_test.go
@@ -18,7 +18,6 @@
 	"encoding/json"
 	"errors"
 	"fmt"
-	"internal/synctest"
 	"internal/testenv"
 	"io"
 	"log"
@@ -44,6 +43,7 @@
 	"sync/atomic"
 	"syscall"
 	"testing"
+	"testing/synctest"
 	"time"
 )
 
@@ -7648,3 +7648,17 @@
 		t.Fatalf("after running test: original NextProtos slice = %v, want %v", nextProtos, wantNextProtos)
 	}
 }
+
+// Verifies that starting a server with HTTP/2 disabled and an empty TLSConfig does not panic.
+// (Tests fix in CL 758560.)
+func TestServerHTTP2Disabled(t *testing.T) {
+	synctest.Test(t, func(t *testing.T) {
+		li := fakeNetListen()
+		srv := &Server{}
+		srv.Protocols = new(Protocols)
+		srv.Protocols.SetHTTP1(true)
+		go srv.ServeTLS(li, "", "")
+		synctest.Wait()
+		srv.Shutdown(t.Context())
+	})
+}