diff --git a/lz4diff/lz4diff_unittest.cc b/lz4diff/lz4diff_unittest.cc
new file mode 100644
index 0000000..aabff99
--- /dev/null
+++ b/lz4diff/lz4diff_unittest.cc
@@ -0,0 +1,110 @@
+//
+// Copyright (C) 2021 The Android Open Source Project
+//
+// 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 <unistd.h>
+
+#include <algorithm>
+#include <mutex>
+#include <string>
+#include <vector>
+
+#include <base/format_macros.h>
+#include <base/logging.h>
+#include <base/strings/string_number_conversions.h>
+#include <base/strings/string_util.h>
+#include <base/strings/stringprintf.h>
+#include <gtest/gtest.h>
+#include <erofs/internal.h>
+#include <erofs/io.h>
+
+#include "lz4diff/lz4diff.h"
+#include "lz4diff/lz4patch.h"
+#include "update_engine/common/test_utils.h"
+#include "update_engine/common/utils.h"
+#include "update_engine/lz4diff/lz4diff_compress.h"
+#include "update_engine/payload_generator/delta_diff_generator.h"
+#include "update_engine/payload_generator/erofs_filesystem.h"
+#include "update_engine/payload_generator/extent_utils.h"
+
+using std::string;
+using std::vector;
+
+namespace chromeos_update_engine {
+
+namespace {
+class Lz4diffTest : public ::testing::Test {};
+
+using test_utils::GetBuildArtifactsPath;
+
+// This test parses the sample images generated during build time with the
+// "generate_image.sh" script. The expected conditions of each file in these
+// images is encoded in the file name, as defined in the mentioned script.
+TEST_F(Lz4diffTest, DiffElfBinary) {
+  const auto old_img = GetBuildArtifactsPath("gen/erofs.img");
+  const auto new_img = GetBuildArtifactsPath("gen/erofs_new.img");
+  auto old_fs = ErofsFilesystem::CreateFromFile(old_img);
+  ASSERT_NE(old_fs, nullptr);
+  ASSERT_EQ(kBlockSize, old_fs->GetBlockSize());
+  auto new_fs = ErofsFilesystem::CreateFromFile(new_img);
+  ASSERT_NE(new_fs, nullptr);
+  ASSERT_EQ(kBlockSize, new_fs->GetBlockSize());
+
+  vector<ErofsFilesystem::File> old_files;
+  ASSERT_TRUE(old_fs->GetFiles(&old_files));
+  vector<ErofsFilesystem::File> new_files;
+  ASSERT_TRUE(new_fs->GetFiles(&new_files));
+
+  const auto it =
+      std::find_if(old_files.begin(), old_files.end(), [](const auto& file) {
+        return file.name == "/delta_generator";
+      });
+  ASSERT_NE(it, old_files.end())
+      << "There should be a delta_generator entry in gen/erofs.img. Is the "
+         "generate_test_erofs_imgages.sh script implemented wrong?";
+  const auto new_it =
+      std::find_if(new_files.begin(), new_files.end(), [](const auto& file) {
+        return file.name == "/delta_generator";
+      });
+  ASSERT_NE(new_it, new_files.end())
+      << "There should be a delta_generator entry in gen/erofs_new.img. Is the "
+         "generate_test_erofs_imgages.sh script implemented wrong?";
+
+  const auto old_delta_generator = *it;
+  auto new_delta_generator = *new_it;
+  Blob old_data;
+  ASSERT_TRUE(utils::ReadExtents(
+      old_img, old_delta_generator.extents, &old_data, kBlockSize));
+  Blob new_data;
+  ASSERT_TRUE(utils::ReadExtents(
+      new_img, new_delta_generator.extents, &new_data, kBlockSize));
+  // New image is actually generated with compression level 7, we use a
+  // different compression level so that recompressed blob is different. This
+  // way we can test the postfix functionality.
+  new_delta_generator.compressed_file_info.algo.set_level(5);
+  Blob diff_blob;
+  ASSERT_TRUE(Lz4Diff(old_data,
+                      new_data,
+                      old_delta_generator.compressed_file_info,
+                      new_delta_generator.compressed_file_info,
+                      &diff_blob));
+  Blob patched_new_data;
+  ASSERT_TRUE(Lz4Patch(old_data, diff_blob, &patched_new_data));
+  ASSERT_EQ(patched_new_data, new_data);
+}
+
+}  // namespace
+
+}  // namespace chromeos_update_engine