Create download_test and add test for Binary downloads not colliding.

go.mod

@@ -26,6 +26,7 @@ require (
 	github.com/docker/machine v0.16.2
 	github.com/elazarl/goproxy v0.0.0-20190421051319-9d40249d3c2f
 	github.com/elazarl/goproxy/ext v0.0.0-20190421051319-9d40249d3c2f // indirect
+	github.com/go-logr/logr v0.4.0
 	github.com/golang-collections/collections v0.0.0-20130729185459-604e922904d3
 	github.com/google/go-cmp v0.5.5
 	github.com/google/go-containerregistry v0.4.1

pkg/minikube/download/binary.go

@@ -52,7 +52,7 @@ func Binary(binary, version, osName, archName string) (string, error) {
 		return "", err
 	}
 
-	if _, err := os.Stat(targetFilepath); err == nil {
+	if _, err := checkCache(targetFilepath); err == nil {
 		klog.Infof("Not caching binary, using %s", url)
 		return targetFilepath, nil
 	}

pkg/minikube/download/download.go

@@ -30,7 +30,8 @@ import (
 )
 
 var (
-	mockMode = false
+	mockMode   = false
+	checkCache = os.Stat
 )
 
 // EnableMock allows tests to selectively enable if downloads are mocked

pkg/minikube/download/download_test.go

@@ -0,0 +1,95 @@
+/*
+Copyright 2020 The Kubernetes Authors All rights reserved.
+
+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 download
+
+import (
+	"fmt"
+	"io/fs"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/go-logr/logr"
+	"k8s.io/klog/v2"
+)
+
+type mockLogger struct {
+	downloads int
+	t         *testing.T
+}
+
+func (ml *mockLogger) Enabled() bool {
+	return true
+}
+func (ml *mockLogger) Info(msg string, keysAndValues ...interface{}) {
+	fmt.Println("hi - ", msg)
+	if strings.Contains(msg, "Mock download") {
+		// Make "downloads" take longer to increase lock time.
+		dur, err := time.ParseDuration("1s")
+		if err != nil {
+			ml.t.Errorf("Could not parse 1 second duration - should never happen")
+		}
+		time.Sleep(dur)
+
+		ml.downloads++
+	}
+}
+func (ml *mockLogger) Error(err error, msg string, keysAndValues ...interface{}) {}
+func (ml *mockLogger) V(level int) logr.Logger {
+	return ml
+}
+func (ml *mockLogger) WithValues(keysAndValues ...interface{}) logr.Logger {
+	return ml
+}
+func (ml *mockLogger) WithName(name string) logr.Logger {
+	return ml
+}
+
+func TestBinaryDownloadPreventsMultipleDownload(t *testing.T) {
+	EnableMock(true)
+	defer EnableMock(false)
+	tlog := &mockLogger{downloads: 0, t: t}
+
+	klog.SetLogger(tlog)
+	defer klog.SetLogger(nil)
+
+	checkCache = func(file string) (fs.FileInfo, error) {
+		if tlog.downloads == 0 {
+			return nil, fmt.Errorf("some error")
+		}
+		return nil, nil
+	}
+
+	var group sync.WaitGroup
+	group.Add(2)
+	dlCall := func() {
+		if _, err := Binary("kubectl", "v1.20.2", "linux", "amd64"); err != nil {
+			t.Errorf("Failed to download binary: %+v", err)
+		}
+		group.Done()
+	}
+
+	go dlCall()
+	go dlCall()
+
+	group.Wait()
+
+	if tlog.downloads != 1 {
+		t.Errorf("Wrong number of downloads occurred. Actual: %v, Expected: 1", tlog.downloads)
+	}
+}