Add unit test for goutil package

internal/goutil/examples_test.go

@@ -146,7 +146,8 @@ func ExampleInstall() {
 	// Install installs an executable from a Go package.
 	err := goutil.Install("example.com/unknown_user/unknown_package")
 
-	// If the package is not found or invalid, Install returns an error
+	// If the package is not found or invalid, Install returns an error.
+	// In this case it should be an error.
 	if err == nil {
 		log.Fatal("example Install failed. non existing/invalid package should return error")
 	}

internal/goutil/goutil.go

@@ -14,6 +14,18 @@ import (
 	"github.com/nao1215/gup/internal/print"
 )
 
+// Internal variables to mock/monkey-patch behaviors in tests.
+var (
+	// goExe is the executable name for the go command.
+	goExe = "go"
+	// keyGoBin is the key name of the env variable for "GOBIN".
+	keyGoBin = "GOBIN"
+	// keyGoPath is the key name of the env variable for "GOPATH".
+	keyGoPath = "GOPATH"
+	// osMkdirTemp is a copy of os.MkdirTemp to ease testing.
+	osMkdirTemp = os.MkdirTemp
+)
+
 // GoPaths has $GOBIN and $GOPATH
 type GoPaths struct {
 	// GOBIN is $GOBIN
@@ -100,17 +112,17 @@ func NewGoPaths() *GoPaths {
 
 // StartDryRunMode change the GOBIN or GOPATH settings to install the binaries in the temporary directory.
 func (gp *GoPaths) StartDryRunMode() error {
-	tmpDir, err := os.MkdirTemp("", "")
+	tmpDir, err := osMkdirTemp("", "")
 	if err != nil {
 		return err
 	}
 
 	if gp.GOBIN != "" {
-		if err := os.Setenv("GOBIN", tmpDir); err != nil {
+		if err := os.Setenv(keyGoBin, tmpDir); err != nil {
 			return err
 		}
 	} else if gp.GOPATH != "" {
-		if err := os.Setenv("GOPATH", tmpDir); err != nil {
+		if err := os.Setenv(keyGoPath, tmpDir); err != nil {
 			return err
 		}
 	} else {
@@ -122,11 +134,11 @@ func (gp *GoPaths) StartDryRunMode() error {
 // EndDryRunMode restore the GOBIN or GOPATH settings.
 func (gp *GoPaths) EndDryRunMode() error {
 	if gp.GOBIN != "" {
-		if err := os.Setenv("GOBIN", gp.GOBIN); err != nil {
+		if err := os.Setenv(keyGoBin, gp.GOBIN); err != nil {
 			return err
 		}
 	} else if gp.GOPATH != "" {
-		if err := os.Setenv("GOPATH", gp.GOPATH); err != nil {
+		if err := os.Setenv(keyGoPath, gp.GOPATH); err != nil {
 			return err
 		}
 	} else {
@@ -151,7 +163,7 @@ func (gp *GoPaths) removeTmpDir() error {
 
 // CanUseGoCmd check whether go command install in the system.
 func CanUseGoCmd() error {
-	_, err := exec.LookPath("go")
+	_, err := exec.LookPath(goExe)
 	return err
 }
 
@@ -160,15 +172,15 @@ func Install(importPath string) error {
 	if importPath == "command-line-arguments" {
 		return errors.New("is devel-binary copied from local environment")
 	}
-	if err := exec.Command("go", "install", importPath+"@latest").Run(); err != nil {
+	if err := exec.Command(goExe, "install", importPath+"@latest").Run(); err != nil {
 		return fmt.Errorf("can't install %s: %w", importPath, err)
 	}
 	return nil
 }
 
 // GetLatestVer execute "$ go list -m -f {{.Version}} <importPath>@latest"
 func GetLatestVer(modulePath string) (string, error) {
-	out, err := exec.Command("go", "list", "-m", "-f", "{{.Version}}", modulePath+"@latest").Output()
+	out, err := exec.Command(goExe, "list", "-m", "-f", "{{.Version}}", modulePath+"@latest").Output()
 	if err != nil {
 		return "", errors.New("can't check " + modulePath)
 	}
@@ -177,7 +189,7 @@ func GetLatestVer(modulePath string) (string, error) {
 
 // goPath return GOPATH environment variable.
 func goPath() string {
-	gopath := os.Getenv("GOPATH")
+	gopath := os.Getenv(keyGoPath)
 	if gopath != "" {
 		return gopath
 	}
@@ -186,7 +198,7 @@ func goPath() string {
 
 // goBin return GOBIN environment variable.
 func goBin() string {
-	return os.Getenv("GOBIN")
+	return os.Getenv(keyGoBin)
 }
 
 // GoBin return $GOPATH/bin directory path.
@@ -205,7 +217,7 @@ func GoBin() (string, error) {
 
 // GoVersionWithOptionM return result of "$ go version -m"
 func GoVersionWithOptionM(bin string) ([]string, error) {
-	out, err := exec.Command("go", "version", "-m", bin).Output()
+	out, err := exec.Command(goExe, "version", "-m", bin).Output()
 	if err != nil {
 		return nil, err
 	}