net/http/cookiejar: added simple example test

Fixes #16884
Updates #16360

Change-Id: I01563031a1c105e54499134eed4789f6219f41ec
Reviewed-on: https://go-review.googlesource.com/27993Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/cookiejar/dummy_publicsuffix_test.go

+// Copyright 2016 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 cookiejar_test
+
+import "net/http/cookiejar"
+
+type dummypsl struct {
+	List cookiejar.PublicSuffixList
+}
+
+func (dummypsl) PublicSuffix(domain string) string {
+	return domain
+}
+
+func (dummypsl) String() string {
+	return "dummy"
+}
+
+var publicsuffix = dummypsl{}

src/net/http/cookiejar/example_test.go

+// Copyright 2016 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 cookiejar_test
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"net/http/cookiejar"
+	"net/http/httptest"
+	"net/url"
+)
+
+func ExampleNew() {
+	// Start a server to give us cookies.
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if cookie, err := r.Cookie("Flavor"); err != nil {
+			http.SetCookie(w, &http.Cookie{Name: "Flavor", Value: "Chocolate Chip"})
+		} else {
+			cookie.Value = "Oatmeal Raisin"
+			http.SetCookie(w, cookie)
+		}
+	}))
+	defer ts.Close()
+
+	u, err := url.Parse(ts.URL)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// All users of cookiejar should import "golang.org/x/net/publicsuffix"
+	jar, err := cookiejar.New(&cookiejar.Options{PublicSuffixList: publicsuffix.List})
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	client := &http.Client{
+		Jar: jar,
+	}
+
+	if _, err = client.Get(u.String()); err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println("After 1st request:")
+	for _, cookie := range jar.Cookies(u) {
+		fmt.Printf("  %s: %s\n", cookie.Name, cookie.Value)
+	}
+
+	if _, err = client.Get(u.String()); err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println("After 2nd request:")
+	for _, cookie := range jar.Cookies(u) {
+		fmt.Printf("  %s: %s\n", cookie.Name, cookie.Value)
+	}
+	// Output:
+	// After 1st request:
+	//   Flavor: Chocolate Chip
+	// After 2nd request:
+	//   Flavor: Oatmeal Raisin
+}