Add end-to-end replication/restore testing

internal/testingutil/testingutil.go

@@ -1,12 +1,13 @@
 package testingutil
 
 import (
+	"io"
 	"os"
 	"testing"
 )
 
-// MustReadFile reads all data from filename. Fail on error.
-func MustReadFile(tb testing.TB, filename string) []byte {
+// ReadFile reads all data from filename. Fail on error.
+func ReadFile(tb testing.TB, filename string) []byte {
 	tb.Helper()
 	b, err := os.ReadFile(filename)
 	if err != nil {
@@ -15,6 +16,26 @@ func MustReadFile(tb testing.TB, filename string) []byte {
 	return b
 }
 
+// CopyFile copies all data from src to dst. Fail on error.
+func CopyFile(tb testing.TB, src, dst string) {
+	tb.Helper()
+	r, err := os.Open(src)
+	if err != nil {
+		tb.Fatal(err)
+	}
+	defer r.Close()
+
+	w, err := os.Create(dst)
+	if err != nil {
+		tb.Fatal(err)
+	}
+	defer w.Close()
+
+	if _, err := io.Copy(w, r); err != nil {
+		tb.Fatal(err)
+	}
+}
+
 // Getpwd returns the working directory. Fail on error.
 func Getwd(tb testing.TB) string {
 	tb.Helper()