diff --git a/src/limestone/dblogutil/dblogutil.cpp b/src/limestone/dblogutil/dblogutil.cpp
index 0142e2fe..bcb544de 100644
--- a/src/limestone/dblogutil/dblogutil.cpp
+++ b/src/limestone/dblogutil/dblogutil.cpp
@@ -163,25 +163,6 @@ void repair(dblog_scan &ds, std::optional<epoch_id_type> epoch) {
     }
 }
 
-static boost::filesystem::path make_tmp_dir_next_to(const boost::filesystem::path& target_dir, const char* suffix) {
-    auto canonicalpath = boost::filesystem::canonical(target_dir);
-    // some versions of boost::filesystem::canonical do not remove trailing directory-separators ('/')
-    std::string targetdirstring = canonicalpath.string();
-    std::size_t prev_len{};
-    do {
-        prev_len = targetdirstring.size();
-        canonicalpath.remove_trailing_separator();  // remove only one char
-        targetdirstring = canonicalpath.string();
-    } while (targetdirstring.size() < prev_len);
-
-    auto tmpdirname = targetdirstring + suffix;
-    if (::mkdtemp(tmpdirname.data()) == nullptr) {
-        LOG_LP(ERROR) << "mkdtemp failed, errno = " << errno;
-        throw std::runtime_error("I/O error");
-    }
-    return {tmpdirname};
-}
-
 static boost::filesystem::path make_work_dir_next_to(const boost::filesystem::path& target_dir) {
     // assume: already checked existence and is_dir
     return make_tmp_dir_next_to(target_dir, ".work_XXXXXX");
diff --git a/src/limestone/filepath.cpp b/src/limestone/filepath.cpp
new file mode 100644
index 00000000..b4d04fde
--- /dev/null
+++ b/src/limestone/filepath.cpp
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2024-2024 Project Tsurugi.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <glog/logging.h>
+#include <limestone/logging.h>
+#include "logging_helper.h"
+
+#include "internal.h"
+
+namespace limestone::internal {
+
+boost::filesystem::path make_tmp_dir_next_to(const boost::filesystem::path& target_dir, const char* suffix) {
+    auto canonicalpath = boost::filesystem::canonical(target_dir);
+    // some versions of boost::filesystem::canonical do not remove trailing directory-separators ('/')
+    std::string targetdirstring = canonicalpath.string();
+    std::size_t prev_len{};
+    do {
+        prev_len = targetdirstring.size();
+        canonicalpath.remove_trailing_separator();  // remove only one char
+        targetdirstring = canonicalpath.string();
+    } while (targetdirstring.size() < prev_len);
+
+    auto tmpdirname = targetdirstring + suffix;
+    if (::mkdtemp(tmpdirname.data()) == nullptr) {
+        LOG_LP(ERROR) << "mkdtemp failed, errno = " << errno;
+        throw std::runtime_error("I/O error");
+    }
+    return {tmpdirname};
+}
+
+}
diff --git a/src/limestone/internal.h b/src/limestone/internal.h
index 3de4e6af..1aea9c6d 100644
--- a/src/limestone/internal.h
+++ b/src/limestone/internal.h
@@ -68,4 +68,8 @@ void create_compact_pwal(
     int num_worker,
     const std::set<std::string>& file_names = std::set<std::string>());
 
+// filepath.cpp
+
+boost::filesystem::path make_tmp_dir_next_to(const boost::filesystem::path& target_dir, const char* suffix);
+
 }
diff --git a/test/limestone/utils/make_tmp_test.cpp b/test/limestone/utils/make_tmp_test.cpp
new file mode 100644
index 00000000..2cd008c8
--- /dev/null
+++ b/test/limestone/utils/make_tmp_test.cpp
@@ -0,0 +1,58 @@
+
+#include <boost/filesystem.hpp>
+
+#include "dblog_scan.h"
+#include "internal.h"
+#include "log_entry.h"
+
+#include "test_root.h"
+
+namespace limestone::testing {
+
+using namespace std::literals;
+using namespace limestone::api;
+using namespace limestone::internal;
+
+class make_tmp_test : public ::testing::Test {
+public:
+static constexpr const char* location = "/tmp/make_tmp_test";
+
+    void SetUp() {
+        boost::filesystem::remove_all(location);
+        if (!boost::filesystem::create_directory(location)) {
+            std::cerr << "cannot make directory" << std::endl;
+        }
+    }
+
+    void TearDown() {
+        boost::filesystem::remove_all(location);
+    }
+
+    bool starts_with(std::string a, std::string b) { return a.substr(0, b.length()) == b; }
+
+};
+
+TEST_F(make_tmp_test, make_tmp_dir_next_to_0slash) {
+    std::string p = std::string(location) + "/test0";
+    boost::filesystem::create_directory(p);
+    auto tmp = make_tmp_dir_next_to({p}, ".suffix_XXXXXX");
+    ASSERT_TRUE(starts_with(tmp.filename().string(), "test0.suffix_"));
+}
+
+// check removing trailig slashes
+
+TEST_F(make_tmp_test, make_tmp_dir_next_to_1slash) {
+    std::string p = std::string(location) + "/test1/";
+    boost::filesystem::create_directory(p);
+    auto tmp = make_tmp_dir_next_to({p}, ".suffix_XXXXXX");
+    ASSERT_TRUE(starts_with(tmp.filename().string(), "test1.suffix_"));
+}
+
+TEST_F(make_tmp_test, make_tmp_dir_next_to_2slash) {
+    std::string p = std::string(location) + "/test2//";
+    boost::filesystem::create_directory(p);
+    auto tmp = make_tmp_dir_next_to({p}, ".suffix_XXXXXX");
+    ASSERT_TRUE(starts_with(tmp.filename().string(), "test2.suffix_"));
+}
+
+}