client-go exec: fix metrics related to plugin not found

These were missed because our tests did not pass in the correct test
data input (the command to execute).

Signed-off-by: Monis Khan <mok@vmware.com>

Kubernetes-commit: a6ac42082b4d7c0057b52900736bd7fbc2c44241

plugin/pkg/client/auth/exec/metrics.go

@@ -18,6 +18,7 @@ package exec
 
 import (
 	"errors"
+	"io/fs"
 	"os/exec"
 	"reflect"
 	"sync"
@@ -92,14 +93,15 @@ func (c *certificateExpirationTracker) set(a *Authenticator, t time.Time) {
 func incrementCallsMetric(err error) {
 	execExitError := &exec.ExitError{}
 	execError := &exec.Error{}
+	pathError := &fs.PathError{}
 	switch {
 	case err == nil: // Binary execution succeeded.
 		metrics.ExecPluginCalls.Increment(successExitCode, noError)
 
 	case errors.As(err, &execExitError): // Binary execution failed (see "os/exec".Cmd.Run()).
 		metrics.ExecPluginCalls.Increment(execExitError.ExitCode(), pluginExecutionError)
 
-	case errors.As(err, &execError): // Binary does not exist (see exec.Error).
+	case errors.As(err, &execError), errors.As(err, &pathError): // Binary does not exist (see exec.Error, fs.PathError).
 		metrics.ExecPluginCalls.Increment(failureExitCode, pluginNotFoundError)
 
 	default: // We don't know about this error type.

plugin/pkg/client/auth/exec/metrics_test.go

@@ -18,6 +18,7 @@ package exec
 
 import (
 	"fmt"
+	"io"
 	"testing"
 	"time"
 
@@ -147,6 +148,7 @@ func TestCallsMetric(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
+		a.stderr = io.Discard
 
 		// Run refresh creds twice so that our test validates that the metrics are set correctly twice
 		// in a row with the same authenticator.
@@ -172,14 +174,15 @@ func TestCallsMetric(t *testing.T) {
 	// metric values.
 	refreshCreds := func(command string) {
 		c := api.ExecConfig{
-			Command:         "does not exist",
+			Command:         command,
 			APIVersion:      "client.authentication.k8s.io/v1beta1",
 			InteractiveMode: api.IfAvailableExecInteractiveMode,
 		}
 		a, err := newAuthenticator(newCache(), func(_ int) bool { return false }, &c, nil)
 		if err != nil {
 			t.Fatal(err)
 		}
+		a.stderr = io.Discard
 		if err := a.refreshCredsLocked(&clientauthentication.Response{}); err == nil {
 			t.Fatal("expected the authenticator to fail because the plugin does not exist")
 		}