Add a helper func to set a default metric config for unit tests (#1263)

* do not record for empty metric config

* Revert "do not record for empty metric config"

This reverts commit 539a5e4dbb.

* add a comment

* fix typo

* fix tests

* revert

* revert tests

* revert

* fix conflicts

* one more test file

controller/stats_reporter_test.go

@@ -23,6 +23,7 @@ import (
 
 	"go.opencensus.io/stats/view"
 	"knative.dev/pkg/metrics/metricstest"
+	_ "knative.dev/pkg/metrics/testing"
 )
 
 func TestNewStatsReporterErrors(t *testing.T) {

metrics/client_test.go

@@ -58,7 +58,7 @@ func TestClientMetrics(t *testing.T) {
 	metrics.Register(cp.NewLatencyMetric(), cp.NewResultMetric())
 
 	// Reset the metrics configuration to avoid leaked state from other tests.
-	setCurMetricsConfig(nil)
+	InitForTesting()
 
 	views := cp.DefaultViews()
 	if got, want := len(views), 2; got != want {

metrics/memstats_test.go

@@ -36,7 +36,7 @@ func TestMemStatsMetrics(t *testing.T) {
 	msp.Start(ctx, period)
 
 	// Reset the metrics configuration to avoid leaked state from other tests.
-	setCurMetricsConfig(nil)
+	InitForTesting()
 
 	views := msp.DefaultViews()
 	if got, want := len(views), 27; got != want {

metrics/testing.go

@@ -0,0 +1,26 @@
+/*
+Copyright 2020 The Knative Authors
+
+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 metrics
+
+// InitForTesting initialize the necessary global variables for unit tests.
+func InitForTesting() {
+	setCurMetricsConfig(&metricsConfig{
+		backendDestination: Prometheus,
+		component:          "test",
+		domain:             "test",
+	})
+}

metrics/testing/config.go

@@ -24,4 +24,5 @@ import (
 
 func init() {
 	os.Setenv(metrics.DomainEnv, "knative.dev/testing")
+	metrics.InitForTesting()
 }

metrics/workqueue_test.go

@@ -48,7 +48,7 @@ func TestWorkqueueMetrics(t *testing.T) {
 	workqueue.SetProvider(wp)
 
 	// Reset the metrics configuration to avoid leaked state from other tests.
-	setCurMetricsConfig(nil)
+	InitForTesting()
 
 	views := wp.DefaultViews()
 	if got, want := len(views), 7; got != want {

source/source_stats_reporter_test.go

@@ -22,6 +22,7 @@ import (
 
 	"knative.dev/pkg/metrics/metricskey"
 	"knative.dev/pkg/metrics/metricstest"
+	_ "knative.dev/pkg/metrics/testing"
 )
 
 func TestStatsReporter(t *testing.T) {

webhook/admission_integration_test.go

@@ -34,6 +34,7 @@ import (
 	authenticationv1 "k8s.io/api/authentication/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"knative.dev/pkg/metrics/metricstest"
+	_ "knative.dev/pkg/metrics/testing"
 )
 
 type fixedAdmissionController struct {

webhook/stats_reporter_test.go

@@ -24,6 +24,7 @@ import (
 	admissionv1beta1 "k8s.io/api/admission/v1beta1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"knative.dev/pkg/metrics/metricstest"
+	_ "knative.dev/pkg/metrics/testing"
 )
 
 func TestWebhookStatsReporter(t *testing.T) {