os: implement and smoketest os.Setenv

src/os/env.go

@@ -9,6 +9,18 @@ func Getenv(key string) string {
 	return v
 }
 
+func Setenv(key, value string) error {
+	err := syscall.Setenv(key, value)
+	if err != nil {
+		return NewSyscallError("setenv", err)
+	}
+	return nil
+}
+
+func Unsetenv(_ string) error {
+	return ErrNotImplemented
+}
+
 func LookupEnv(key string) (string, bool) {
 	return syscall.Getenv(key)
 }

src/os/env_test.go

@@ -0,0 +1,38 @@
+// Copyright 2010 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.
+
+package os_test
+
+import (
+	. "os"
+	"reflect"
+	"testing"
+)
+
+func TestConsistentEnviron(t *testing.T) {
+	e0 := Environ()
+	for i := 0; i < 10; i++ {
+		e1 := Environ()
+		if !reflect.DeepEqual(e0, e1) {
+			t.Fatalf("environment changed")
+		}
+	}
+}
+
+func TestLookupEnv(t *testing.T) {
+	const smallpox = "SMALLPOX"      // No one has smallpox.
+	value, ok := LookupEnv(smallpox) // Should not exist.
+	if ok || value != "" {
+		t.Fatalf("%s=%q", smallpox, value)
+	}
+	defer Unsetenv(smallpox)
+	err := Setenv(smallpox, "virus")
+	if err != nil {
+		t.Fatalf("failed to release smallpox virus")
+	}
+	_, ok = LookupEnv(smallpox)
+	if !ok {
+		t.Errorf("smallpox release failed; world remains safe but LookupEnv is broken")
+	}
+}