diff --git a/build.docker b/build.docker
index 7895c31..03832db 100644
--- a/build.docker
+++ b/build.docker
@@ -1,7 +1,10 @@
 FROM golang:1.20
 
+# enable backports for git-filter-repo
+RUN echo "deb http://deb.debian.org/debian bullseye-backports main" >> /etc/apt/sources.list.d/backports.list
+
 RUN apt-get update && apt-get install -y \
-    rsync libssl-dev postgresql sudo redis-server \
+    rsync libssl-dev postgresql sudo redis-server git-filter-repo/bullseye-backports \
  && rm -rf /var/lib/apt/lists/*
 
 RUN curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.51.1
diff --git a/tools/testtool/commands/list_private_files.go b/tools/testtool/commands/list_private_files.go
new file mode 100644
index 0000000..a338682
--- /dev/null
+++ b/tools/testtool/commands/list_private_files.go
@@ -0,0 +1,45 @@
+package commands
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/spf13/cobra"
+)
+
+var listPrivateFilesCmd = &cobra.Command{
+	Use:   "list-private-files",
+	Short: "list private files",
+	Run:   runListPrivateFiles,
+}
+
+func init() {
+	rootCmd.AddCommand(listPrivateFilesCmd)
+}
+
+func doListPrivateFiles() error {
+	cwd, err := os.Getwd()
+	if err != nil {
+		return err
+	}
+
+	privateFiles := listPrivateFiles(".")
+	for _, f := range privateFiles {
+		rel, err := filepath.Rel(cwd, f)
+		if err != nil {
+			return err
+		}
+
+		fmt.Println(rel)
+	}
+
+	return nil
+}
+
+func runListPrivateFiles(cmd *cobra.Command, args []string) {
+	if err := doListPrivateFiles(); err != nil {
+		fmt.Fprintf(os.Stderr, "testtool: %v\n", err)
+		os.Exit(1)
+	}
+}