internal/testpty: move from os/signal/internal/pty

We're going to use this for another test, so make it more accessible.

Preparation for #37486.

Change-Id: If194cc4244c4b9e1b1f253759b813555b39ad67e
Reviewed-on: https://go-review.googlesource.com/c/go/+/449502
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/go/build/deps_test.go

@@ -558,7 +558,7 @@ var depsRules = `
 	< internal/obscuretestdata;
 
 	CGO, OS, fmt
-	< os/signal/internal/pty;
+	< internal/testpty;
 
 	NET, testing, math/rand
 	< golang.org/x/net/nettest;

src/internal/testpty/pty.go

@@ -4,10 +4,9 @@
 
 //go:build ((aix || dragonfly || freebsd || (linux && !android) || netbsd || openbsd) && cgo) || darwin
 
-// Package pty is a simple pseudo-terminal package for Unix systems,
+// Package testpty is a simple pseudo-terminal package for Unix systems,
 // implemented by calling C functions via cgo.
-// This is only used for testing the os/signal package.
-package pty
+package testpty
 
 import (
 	"fmt"

src/internal/testpty/pty_cgo.go

@@ -4,7 +4,7 @@
 
 //go:build cgo && (aix || dragonfly || freebsd || (linux && !android) || netbsd || openbsd)
 
-package pty
+package testpty
 
 /*
 #define _XOPEN_SOURCE 600

src/internal/testpty/pty_darwin.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package pty
+package testpty
 
 import (
 	"internal/syscall/unix"

src/os/signal/signal_cgo_test.go

@@ -14,10 +14,10 @@ import (
 	"context"
 	"encoding/binary"
 	"fmt"
+	"internal/testpty"
 	"os"
 	"os/exec"
 	"os/signal"
-	ptypkg "os/signal/internal/pty"
 	"runtime"
 	"strconv"
 	"syscall"
@@ -105,9 +105,9 @@ func TestTerminalSignal(t *testing.T) {
 
 	t.Parallel()
 
-	pty, procTTYName, err := ptypkg.Open()
+	pty, procTTYName, err := testpty.Open()
 	if err != nil {
-		ptyErr := err.(*ptypkg.PtyError)
+		ptyErr := err.(*testpty.PtyError)
 		if ptyErr.FuncName == "posix_openpt" && ptyErr.Errno == syscall.EACCES {
 			t.Skip("posix_openpt failed with EACCES, assuming chroot and skipping")
 		}