http2: add http2wrap test

Add a test which reruns the package tests with -tags=http2wrap,
when the Go version supports it.

For #78508

Change-Id: I4ebf7e676de18f5d33e480e67997727d6a6a6964
Reviewed-on: https://go-review.googlesource.com/c/net/+/771221
Reviewed-by: Nicholas Husin <husin@google.com>
Reviewed-by: Nicholas Husin <nsh@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

http2/wrap_test.go

diff --git a/http2/wrap_test.go b/http2/wrap_test.go
new file mode 100644
index 0000000..b8abb03
--- /dev/null
+++ b/http2/wrap_test.go
@@ -0,0 +1,39 @@
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.27 && !http2wrap
+
+package http2_test
+
+import (
+	"os/exec"
+	"testing"
+)
+
+func TestWrap(t *testing.T) {
+	goTest(t, "-tags=http2wrap", ".")
+}
+
+// TestSuccess is a no-op test for confirming we can re-run "go test".
+func TestSuccess(t *testing.T) {}
+
+func goTest(t *testing.T, args ...string) {
+	goTool, err := exec.LookPath("go")
+	if err != nil {
+		t.Skipf("can't find go tool: %v", err)
+	}
+
+	// Skip this test if we can't run any tests at all.
+	checkCmd := exec.CommandContext(t.Context(), goTool,
+		"test", "-run=^TestSuccess$", ".")
+	if out, err := checkCmd.CombinedOutput(); err != nil {
+		t.Skipf("can't run trivial go test\n%s", out)
+	}
+
+	testCmd := exec.CommandContext(t.Context(), goTool, "test")
+	testCmd.Args = append(testCmd.Args, args...)
+	if out, err := testCmd.CombinedOutput(); err != nil {
+		t.Fatalf("%q failed: %v\n%s", testCmd.Args, err, out)
+	}
+}