tests/integration: Simplify the testMain for examples.

We introduce a LazyCluster abstraction (instead of copy-pasted logic)
that makes clusters to be created only if there are runnable tests
in need for the infrastructure.

client/main_test.go

@@ -21,8 +21,8 @@ import (
 	"go.etcd.io/etcd/v3/pkg/testutil"
 )
 
-var exampleEndpoints []string
-var exampleTransport *http.Transport
+func exampleEndpoints() []string        { return nil }
+func exampleTransport() *http.Transport { return nil }
 
 func forUnitTestsRunInMockedContext(mocking func(), example func()) {
 	mocking()

pkg/testutil/leak.go

@@ -133,6 +133,8 @@ func interestingGoroutines() (gs []string) {
 func MustCheckLeakedGoroutine() {
 	http.DefaultTransport.(*http.Transport).CloseIdleConnections()
 
+	CheckAfterTest(5 * time.Second)
+
 	// Let the other goroutines finalize.
 	runtime.Gosched()
 

tests/integration/client/examples/example_keys_test.go

@@ -34,8 +34,8 @@ func ExampleKeysAPI_directory() {
 		mockKeysAPI_directory,
 		func() {
 			c, err := client.New(client.Config{
-				Endpoints: exampleEndpoints,
-				Transport: exampleTransport,
+				Endpoints: exampleEndpoints(),
+				Transport: exampleTransport(),
 			})
 			if err != nil {
 				log.Fatal(err)
@@ -85,8 +85,8 @@ func ExampleKeysAPI_setget() {
 		mockKeysAPI_setget,
 		func() {
 			c, err := client.New(client.Config{
-				Endpoints: exampleEndpoints,
-				Transport: exampleTransport,
+				Endpoints: exampleEndpoints(),
+				Transport: exampleTransport(),
 			})
 			if err != nil {
 				log.Fatal(err)

tests/integration/client/examples/main_test.go

@@ -15,19 +15,18 @@
 package client_test
 
 import (
-	"fmt"
 	"net/http"
 	"os"
 	"testing"
-	"time"
 
 	"go.etcd.io/etcd/tests/v3/integration"
 	"go.etcd.io/etcd/v3/pkg/testutil"
-	"go.etcd.io/etcd/v3/pkg/transport"
 )
 
-var exampleEndpoints []string
-var exampleTransport *http.Transport
+var lazyCluster = integration.NewLazyCluster()
+
+func exampleEndpoints() []string        { return lazyCluster.EndpointsV2() }
+func exampleTransport() *http.Transport { return lazyCluster.Transport() }
 
 func forUnitTestsRunInMockedContext(mocking func(), example func()) {
 	// For integration tests runs in the provided environment
@@ -36,22 +35,8 @@ func forUnitTestsRunInMockedContext(mocking func(), example func()) {
 
 // TestMain sets up an etcd cluster if running the examples.
 func TestMain(m *testing.M) {
-	tr, trerr := transport.NewTransport(transport.TLSInfo{}, time.Second)
-	if trerr != nil {
-		fmt.Fprintf(os.Stderr, "%v", trerr)
-		os.Exit(1)
-	}
-	cfg := integration.ClusterConfig{Size: 1}
-	clus := integration.NewClusterV3(nil, &cfg)
-	exampleEndpoints = []string{clus.Members[0].URL()}
-	exampleTransport = tr
 	v := m.Run()
-	clus.Terminate(nil)
-	if err := testutil.CheckAfterTest(time.Second); err != nil {
-		fmt.Fprintf(os.Stderr, "%v", err)
-		os.Exit(1)
-	}
-
+	lazyCluster.Terminate()
 	if v == 0 {
 		testutil.MustCheckLeakedGoroutine()
 	}

tests/integration/lazy_cluster.go

@@ -0,0 +1,82 @@
+// Copyright 2020 The etcd 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 integration
+
+import (
+	"log"
+	"net/http"
+	"sync"
+	"time"
+
+	"go.etcd.io/etcd/v3/pkg/transport"
+)
+
+type LazyCluster interface {
+	// EndpointsV2 - call to this method might initialize the cluster.
+	EndpointsV2() []string
+
+	// EndpointsV2 - call to this method might initialize the cluster.
+	EndpointsV3() []string
+
+	// Transport - call to this method might initialize the cluster.
+	Transport() *http.Transport
+
+	Terminate()
+}
+
+type lazyCluster struct {
+	cfg       ClusterConfig
+	cluster   *ClusterV3
+	transport *http.Transport
+	once      sync.Once
+}
+
+// NewLazyCluster returns a new test cluster handler that gets created on the
+// first call to GetEndpoints() or GetTransport()
+func NewLazyCluster() LazyCluster {
+	return &lazyCluster{cfg: ClusterConfig{Size: 1}}
+}
+
+func (lc *lazyCluster) mustLazyInit() {
+	lc.once.Do(func() {
+		var err error
+		lc.transport, err = transport.NewTransport(transport.TLSInfo{}, time.Second)
+		if err != nil {
+			log.Fatal(err)
+		}
+		lc.cluster = NewClusterV3(nil, &lc.cfg)
+	})
+}
+
+func (lc *lazyCluster) Terminate() {
+	if lc != nil {
+		lc.cluster.Terminate(nil)
+	}
+}
+
+func (lc *lazyCluster) EndpointsV2() []string {
+	lc.mustLazyInit()
+	return []string{lc.cluster.Members[0].URL()}
+}
+
+func (lc *lazyCluster) EndpointsV3() []string {
+	lc.mustLazyInit()
+	return []string{lc.cluster.Client(0).Endpoints()[0]}
+}
+
+func (lc *lazyCluster) Transport() *http.Transport {
+	lc.mustLazyInit()
+	return lc.transport
+}