Add a test for creation of anonymous tempfiles

tools/utils/tmpfile_linux.go

@@ -24,7 +24,11 @@ func CreateAnonymousTemp(dir string) (*os.File, error) {
 		return os.NewFile(uintptr(fd), path), nil
 	}
 	if err == unix.ENOENT {
-		return nil, err
+		return nil, &os.PathError{
+			Op:   "open",
+			Path: dir,
+			Err:  err,
+		}
 	}
 	f, err := os.CreateTemp(dir, "")
 	if err != nil {

tools/utils/tpmfile_test.go

@@ -0,0 +1,26 @@
+// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"fmt"
+	"runtime"
+	"strconv"
+	"testing"
+)
+
+var _ = fmt.Print
+
+func TestCreateAnonymousTempfile(t *testing.T) {
+	f, err := CreateAnonymousTemp("")
+	if err != nil {
+		t.Fatal(err)
+	}
+	fd := int64(f.Fd())
+	f.Close()
+	if runtime.GOOS == "linux" {
+		if f.Name() != "/proc/self/fd/"+strconv.FormatInt(fd, 10) {
+			t.Fatalf("Anonymous tempfile was not created atomically")
+		}
+	}
+}