unittests: Skip test if not on GCE

The test in pkg/credentialprovider/gcp/metadata_test.go is meant to
run only on GCE, which means that it will fail in any other case.

We should skip the test if we're not testing in GCE or Windows in GCE.

pkg/credentialprovider/gcp/metadata_test.go

@@ -26,6 +26,7 @@ import (
 	"net/url"
 	"os"
 	"reflect"
+	"runtime"
 	"strings"
 	"testing"
 
@@ -47,6 +48,12 @@ func createProductNameFile() (string, error) {
 // referenced by gceProductNameFile being removed, which is the opposite of
 // the other tests
 func TestMetadata(t *testing.T) {
+	// This test requires onGCEVM to return True. On Linux, this can be faked by creating a
+	// Product Name File. But on Windows, onGCEVM makes the following syscall instead:
+	// wmic computersystem get model
+	if runtime.GOOS == "windows" && !onGCEVM() {
+		t.Skip("Skipping test on Windows, not on GCE.")
+	}
 	var err error
 	gceProductNameFile, err = createProductNameFile()
 	if err != nil {