diff --git a/test/fake_sys_file.hpp b/test/fake_sys_file.hpp
new file mode 100644
index 0000000..1c6a45d
--- /dev/null
+++ b/test/fake_sys_file.hpp
@@ -0,0 +1,63 @@
+#pragma once
+
+#include "sys_file.hpp"
+
+#include <stdint.h>
+
+#include <cstring>
+#include <string>
+#include <vector>
+
+using std::size_t;
+using std::uint16_t;
+using std::uint32_t;
+using std::uint8_t;
+
+using namespace std::string_literals;
+
+namespace binstore
+{
+
+/* An in-memory file implementation to test read/write operations, which works
+ * around the problem that Docker image cannot create file in tmpdir. */
+class FakeSysFile : public SysFile
+{
+  public:
+    size_t readToBuf(size_t pos, size_t count, char* buf) const override
+    {
+        auto result = readAsStr(pos, count);
+        std::copy(result.begin(), result.end(), buf);
+        return result.size();
+    }
+
+    std::string readAsStr(size_t pos, size_t count) const override
+    {
+        if (pos >= data_.size())
+        {
+            return "";
+        }
+
+        return data_.substr(pos, count);
+    }
+
+    std::string readRemainingAsStr(size_t pos) const override
+    {
+        return readAsStr(pos, data_.size());
+    }
+
+    void writeStr(const std::string& data, size_t pos) override
+    {
+        if (pos >= data.size())
+        {
+            return;
+        }
+
+        data_.resize(pos);
+        data_.insert(data_.begin() + pos, data.begin(), data.end());
+    }
+
+  protected:
+    std::string data_ = ""s;
+};
+
+} // namespace binstore