oauth2: Token.Extra should be type agnostic

Change-Id: Ic8496d10de47181f6b9c16360b5101c6314d71ee
Reviewed-on: https://go-review.googlesource.com/1653
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

token_test.go

@@ -0,0 +1,30 @@
+// Copyright 2014 The oauth2 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 oauth2
+
+import "testing"
+
+func TestTokenExtra(t *testing.T) {
+	type testCase struct {
+		key  string
+		val  interface{}
+		want interface{}
+	}
+	const key = "extra-key"
+	cases := []testCase{
+		{key: key, val: "abc", want: "abc"},
+		{key: key, val: 123, want: 123},
+		{key: key, val: "", want: ""},
+		{key: "other-key", val: "def", want: nil},
+	}
+	for _, tc := range cases {
+		extra := make(map[string]interface{})
+		extra[tc.key] = tc.val
+		tok := &Token{raw: extra}
+		if got, want := tok.Extra(key), tc.want; got != want {
+			t.Errorf("Extra(%q) = %q; want %q", key, got, want)
+		}
+	}
+}