Add context-aware "time" library wrapper.

go/src/infra/libs/clock/clockflag/duration_test.go

Index: go/src/infra/libs/clock/clockflag/duration_test.go
diff --git a/go/src/infra/libs/clock/clockflag/duration_test.go b/go/src/infra/libs/clock/clockflag/duration_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..df1583f6b5458bda098db1e963a913f88ff3db0f
--- /dev/null
+++ b/go/src/infra/libs/clock/clockflag/duration_test.go
@@ -0,0 +1,62 @@
+// Copyright 2015 The Chromium 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 clockflag
+
+import (
+	"encoding/json"
+	"flag"
+	"testing"
+	"time"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestDuration(t *testing.T) {
+	Convey(`A Duration flag`, t, func() {
+		fs := flag.NewFlagSet("test", flag.ContinueOnError)
+		var d Duration
+		fs.Var(&d, "duration", "Test duration parameter.")
+
+		Convey(`Parses a 10-second Duration from "10s".`, func() {
+			err := fs.Parse([]string{"-duration", "10s"})
+			So(err, ShouldBeNil)
+			So(d.Duration(), ShouldEqual, time.Second*10)
+			So(d.IsZero(), ShouldBeFalse)
+		})
+
+		Convey(`Returns an error when parsing "10z".`, func() {
+			err := fs.Parse([]string{"-duration", "10z"})
+			So(err, ShouldNotBeNil)
+		})
+
+		Convey(`When treated as a JSON field`, func() {
+			var s struct {
+				D Duration `json:"duration"`
+			}
+
+			testJSON := `{"duration":10}`
+			Convey(`Fails to unmarshal from `+testJSON+`.`, func() {
+				testJSON := testJSON
+				err := json.Unmarshal([]byte(testJSON), &s)
+				So(err, ShouldNotBeNil)
+			})
+
+			Convey(`Marshals correctly to duration string.`, func() {
+				testDuration := (5 * time.Second) + (2 * time.Minute)
+				s.D = Duration(testDuration)
+				testJSON, err := json.Marshal(&s)
+				So(err, ShouldBeNil)
+				So(string(testJSON), ShouldEqual, `{"duration":"2m5s"}`)
+
+				Convey(`And Unmarshals correctly.`, func() {
+					s.D = Duration(0)
+					err := json.Unmarshal([]byte(testJSON), &s)
+					So(err, ShouldBeNil)
+					So(s.D.Duration(), ShouldEqual, testDuration)
+				})
+			})
+		})
+	})
+}