Swap `time.Now with testable Time.Now`.

api/api.go

@@ -2,6 +2,7 @@ package api
 
 import (
 	"code.google.com/p/gorest"
+	"github.com/prometheus/prometheus/utility"
 )
 
 type MetricsService struct {
@@ -9,4 +10,5 @@ type MetricsService struct {
 
 	query      gorest.EndPoint `method:"GET" path:"/query?{expr:string}&{json:string}" output:"string"`
 	queryRange gorest.EndPoint `method:"GET" path:"/query_range?{expr:string}&{end:int64}&{range:int64}&{step:int64}" output:"string"`
+	time       utility.Time
 }

api/query.go

@@ -15,7 +15,7 @@ func (serv MetricsService) Query(Expr string, Json string) (result string) {
 		return ast.ErrorToJSON(err)
 	}
 
-	timestamp := time.Now()
+	timestamp := serv.time.Now()
 
 	rb := serv.ResponseBuilder()
 	var format ast.OutputFormat
@@ -42,7 +42,7 @@ func (serv MetricsService) QueryRange(Expr string, End int64, Range int64, Step
 	rb.SetContentType(gorest.Application_Json)
 
 	if End == 0 {
-		End = time.Now().Unix()
+		End = serv.time.Now().Unix()
 	}
 
 	if Step < 1 {

retrieval/format/processor0_0_1.go

@@ -17,9 +17,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"github.com/prometheus/prometheus/model"
+	"github.com/prometheus/prometheus/utility"
 	"io"
 	"io/ioutil"
-	"time"
 )
 
 const (
@@ -41,6 +41,7 @@ var (
 
 // processor001 is responsible for handling API version 0.0.1.
 type processor001 struct {
+	time utility.Time
 }
 
 // entity001 represents a the JSON structure that 0.0.1 uses.
@@ -72,8 +73,7 @@ func (p *processor001) Process(stream io.ReadCloser, baseLabels model.LabelSet,
 		return
 	}
 
-	// Swap this to the testable timer.
+	now := p.time.Now()
-	now := time.Now()
 
 	// TODO(matt): This outer loop is a great basis for parallelization.
 	for _, entity := range entities {

retrieval/scheduler.go

@@ -14,6 +14,7 @@
 package retrieval
 
 import (
+	"github.com/prometheus/prometheus/utility"
 	"math"
 	"time"
 )
@@ -27,32 +28,6 @@ const (
 	MAXIMUM_BACKOFF_VALUE = 30 * time.Minute
 )
 
-// A basic interface only useful in testing contexts for dispensing the time
-// in a controlled manner.
-type instantProvider interface {
-	// The current instant.
-	Now() time.Time
-}
-
-// timer is a simple means for fluently wrapping around standard Go timekeeping
-// mechanisms to enhance testability without compromising code readability.
-//
-// A timer is sufficient for use on bare initialization.  A provider should be
-// set only for test contexts.  When not provided, a timer emits the current
-// system time.
-type timer struct {
-	// The underlying means through which time is provided, if supplied.
-	provider instantProvider
-}
-
-// Emit the current instant.
-func (t timer) Now() time.Time {
-	if t.provider == nil {
-		return time.Now()
-	}
-	return t.provider.Now()
-}
-
 // scheduler is an interface that various scheduling strategies must fulfill
 // in order to set the scheduling order for a target.
 //
@@ -83,7 +58,7 @@ type scheduler interface {
 type healthScheduler struct {
 	scheduledFor     time.Time
 	target           healthReporter
-	timer            timer
+	time             utility.Time
 	unreachableCount int
 }
 
@@ -138,6 +113,6 @@ func (s *healthScheduler) Reschedule(e time.Time, f TargetState) {
 			backoff = exponential
 		}
 
-		s.scheduledFor = s.timer.Now().Add(backoff)
+		s.scheduledFor = s.time.Now().Add(backoff)
 	}
 }

retrieval/scheduler_test.go

@@ -14,6 +14,7 @@
 package retrieval
 
 import (
+	"github.com/prometheus/prometheus/utility"
 	"github.com/prometheus/prometheus/utility/test"
 	"testing"
 	"time"
@@ -32,19 +33,6 @@ func (h fakeHealthReporter) State() (state TargetState) {
 	return
 }
 
-type fakeTimeProvider struct {
-	index     int
-	timeQueue []time.Time
-}
-
-func (t *fakeTimeProvider) Now() (time time.Time) {
-	time = t.timeQueue[t.index]
-
-	t.index++
-
-	return
-}
-
 func testHealthScheduler(t test.Tester) {
 	now := time.Now()
 	var scenarios = []struct {
@@ -77,10 +65,7 @@ func testHealthScheduler(t test.Tester) {
 	}
 
 	for i, scenario := range scenarios {
-		provider := &fakeTimeProvider{}
+		provider := test.NewInstantProvider(scenario.preloadedTimes)
-		for _, time := range scenario.preloadedTimes {
-			provider.timeQueue = append(provider.timeQueue, time)
-		}
 
 		reporter := fakeHealthReporter{}
 		for _, state := range scenario.futureHealthState {
@@ -90,12 +75,12 @@ func testHealthScheduler(t test.Tester) {
 			t.Fatalf("%d. times and health reports and next time lengths were not equal.", i)
 		}
 
-		timer := timer{
+		time := utility.Time{
-			provider: provider,
+			Provider: provider,
 		}
 
 		scheduler := healthScheduler{
-			timer:        timer,
+			time:         time,
 			target:       reporter,
 			scheduledFor: now,
 		}

utility/test/time.go

@@ -0,0 +1,42 @@
+// Copyright 2013 Prometheus Team
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package test
+
+import (
+	"github.com/prometheus/prometheus/utility"
+	"time"
+)
+
+type instantProvider struct {
+	index     int
+	timeQueue []time.Time
+}
+
+func (t *instantProvider) Now() (time time.Time) {
+	time = t.timeQueue[t.index]
+
+	t.index++
+
+	return
+}
+
+// NewInstantProvider furnishes an InstantProvider with prerecorded responses
+// for calls made against it.  It has no validation behaviors of its own and
+// will panic if times are requested more than available pre-recorded behaviors.
+func NewInstantProvider(times []time.Time) utility.InstantProvider {
+	return &instantProvider{
+		index:     0,
+		timeQueue: times,
+	}
+}

utility/time.go

@@ -0,0 +1,45 @@
+// Copyright 2013 Prometheus Team
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package utility
+
+import (
+	"time"
+)
+
+// A basic interface only useful in testing contexts for dispensing the time
+// in a controlled manner.
+type InstantProvider interface {
+	// The current instant.
+	Now() time.Time
+}
+
+// Time is a simple means for fluently wrapping around standard Go timekeeping
+// mechanisms to enhance testability without compromising code readability.
+//
+// It is sufficient for use on bare initialization.  A provider should be
+// set only for test contexts.  When not provided, it emits the current
+// system time.
+type Time struct {
+	// The underlying means through which time is provided, if supplied.
+	Provider InstantProvider
+}
+
+// Emit the current instant.
+func (t Time) Now() time.Time {
+	if t.Provider == nil {
+		return time.Now()
+	}
+
+	return t.Provider.Now()
+}