diff --git a/tests/unit/applypatch_test.cpp b/tests/unit/applypatch_test.cpp
new file mode 100644
index 0000000..4fbdd37
--- /dev/null
+++ b/tests/unit/applypatch_test.cpp
@@ -0,0 +1,303 @@
+/*
+ * Copyright (C) 2016 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 agree 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 <dirent.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <time.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/stringprintf.h>
+#include <android-base/test_utils.h>
+#include <android-base/unique_fd.h>
+#include <gtest/gtest.h>
+#include <openssl/sha.h>
+
+#include "applypatch/applypatch.h"
+#include "common/test_constants.h"
+#include "otautil/paths.h"
+#include "otautil/print_sha1.h"
+
+using namespace std::string_literals;
+
+static void sha1sum(const std::string& fname, std::string* sha1, size_t* fsize = nullptr) {
+  ASSERT_TRUE(sha1 != nullptr);
+
+  std::string data;
+  ASSERT_TRUE(android::base::ReadFileToString(fname, &data));
+
+  if (fsize != nullptr) {
+    *fsize = data.size();
+  }
+
+  uint8_t digest[SHA_DIGEST_LENGTH];
+  SHA1(reinterpret_cast<const uint8_t*>(data.c_str()), data.size(), digest);
+  *sha1 = print_sha1(digest);
+}
+
+static void mangle_file(const std::string& fname) {
+  std::string content(1024, '\0');
+  for (size_t i = 0; i < 1024; i++) {
+    content[i] = rand() % 256;
+  }
+  ASSERT_TRUE(android::base::WriteStringToFile(content, fname));
+}
+
+class ApplyPatchTest : public ::testing::Test {
+ public:
+  void SetUp() override {
+    // set up files
+    old_file = from_testdata_base("old.file");
+    new_file = from_testdata_base("new.file");
+    nonexistent_file = from_testdata_base("nonexistent.file");
+
+    // set up SHA constants
+    sha1sum(old_file, &old_sha1, &old_size);
+    sha1sum(new_file, &new_sha1, &new_size);
+    srand(time(nullptr));
+    bad_sha1_a = android::base::StringPrintf("%040x", rand());
+    bad_sha1_b = android::base::StringPrintf("%040x", rand());
+  }
+
+  std::string old_file;
+  std::string new_file;
+  std::string nonexistent_file;
+
+  std::string old_sha1;
+  std::string new_sha1;
+  std::string bad_sha1_a;
+  std::string bad_sha1_b;
+
+  size_t old_size;
+  size_t new_size;
+};
+
+TEST_F(ApplyPatchTest, CheckModeSkip) {
+  std::vector<std::string> sha1s;
+  ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
+}
+
+TEST_F(ApplyPatchTest, CheckModeSingle) {
+  std::vector<std::string> sha1s = { old_sha1 };
+  ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
+}
+
+TEST_F(ApplyPatchTest, CheckModeMultiple) {
+  std::vector<std::string> sha1s = { bad_sha1_a, old_sha1, bad_sha1_b };
+  ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
+}
+
+TEST_F(ApplyPatchTest, CheckModeFailure) {
+  std::vector<std::string> sha1s = { bad_sha1_a, bad_sha1_b };
+  ASSERT_NE(0, applypatch_check(&old_file[0], sha1s));
+}
+
+TEST_F(ApplyPatchTest, CheckModeEmmcTarget) {
+  // EMMC:old_file:size:sha1 should pass the check.
+  std::string src_file = "EMMC:" + old_file + ":" + std::to_string(old_size) + ":" + old_sha1;
+  std::vector<std::string> sha1s;
+  ASSERT_EQ(0, applypatch_check(src_file.c_str(), sha1s));
+
+  // EMMC:old_file:(size-1):sha1:(size+1):sha1 should fail the check.
+  src_file = "EMMC:" + old_file + ":" + std::to_string(old_size - 1) + ":" + old_sha1 + ":" +
+             std::to_string(old_size + 1) + ":" + old_sha1;
+  ASSERT_EQ(1, applypatch_check(src_file.c_str(), sha1s));
+
+  // EMMC:old_file:(size-1):sha1:size:sha1:(size+1):sha1 should pass the check.
+  src_file = "EMMC:" + old_file + ":" + std::to_string(old_size - 1) + ":" + old_sha1 + ":" +
+             std::to_string(old_size) + ":" + old_sha1 + ":" + std::to_string(old_size + 1) + ":" +
+             old_sha1;
+  ASSERT_EQ(0, applypatch_check(src_file.c_str(), sha1s));
+
+  // EMMC:old_file:(size+1):sha1:(size-1):sha1:size:sha1 should pass the check.
+  src_file = "EMMC:" + old_file + ":" + std::to_string(old_size + 1) + ":" + old_sha1 + ":" +
+             std::to_string(old_size - 1) + ":" + old_sha1 + ":" + std::to_string(old_size) + ":" +
+             old_sha1;
+  ASSERT_EQ(0, applypatch_check(src_file.c_str(), sha1s));
+
+  // EMMC:new_file:(size+1):old_sha1:(size-1):old_sha1:size:old_sha1:size:new_sha1
+  // should pass the check.
+  src_file = "EMMC:" + new_file + ":" + std::to_string(old_size + 1) + ":" + old_sha1 + ":" +
+             std::to_string(old_size - 1) + ":" + old_sha1 + ":" + std::to_string(old_size) + ":" +
+             old_sha1 + ":" + std::to_string(new_size) + ":" + new_sha1;
+  ASSERT_EQ(0, applypatch_check(src_file.c_str(), sha1s));
+}
+
+class ApplyPatchCacheTest : public ApplyPatchTest {
+ protected:
+  void SetUp() override {
+    ApplyPatchTest::SetUp();
+    Paths::Get().set_cache_temp_source(old_file);
+  }
+};
+
+TEST_F(ApplyPatchCacheTest, CheckCacheCorruptedSourceSingle) {
+  TemporaryFile temp_file;
+  mangle_file(temp_file.path);
+  std::vector<std::string> sha1s_single = { old_sha1 };
+  ASSERT_EQ(0, applypatch_check(temp_file.path, sha1s_single));
+  ASSERT_EQ(0, applypatch_check(nonexistent_file.c_str(), sha1s_single));
+}
+
+TEST_F(ApplyPatchCacheTest, CheckCacheCorruptedSourceMultiple) {
+  TemporaryFile temp_file;
+  mangle_file(temp_file.path);
+  std::vector<std::string> sha1s_multiple = { bad_sha1_a, old_sha1, bad_sha1_b };
+  ASSERT_EQ(0, applypatch_check(temp_file.path, sha1s_multiple));
+  ASSERT_EQ(0, applypatch_check(nonexistent_file.c_str(), sha1s_multiple));
+}
+
+TEST_F(ApplyPatchCacheTest, CheckCacheCorruptedSourceFailure) {
+  TemporaryFile temp_file;
+  mangle_file(temp_file.path);
+  std::vector<std::string> sha1s_failure = { bad_sha1_a, bad_sha1_b };
+  ASSERT_NE(0, applypatch_check(temp_file.path, sha1s_failure));
+  ASSERT_NE(0, applypatch_check(nonexistent_file.c_str(), sha1s_failure));
+}
+
+class FreeCacheTest : public ::testing::Test {
+ protected:
+  static constexpr size_t PARTITION_SIZE = 4096 * 10;
+
+  // Returns a sorted list of files in |dirname|.
+  static std::vector<std::string> FindFilesInDir(const std::string& dirname) {
+    std::vector<std::string> file_list;
+
+    std::unique_ptr<DIR, decltype(&closedir)> d(opendir(dirname.c_str()), closedir);
+    struct dirent* de;
+    while ((de = readdir(d.get())) != 0) {
+      std::string path = dirname + "/" + de->d_name;
+
+      struct stat st;
+      if (stat(path.c_str(), &st) == 0 && S_ISREG(st.st_mode)) {
+        file_list.emplace_back(de->d_name);
+      }
+    }
+
+    std::sort(file_list.begin(), file_list.end());
+    return file_list;
+  }
+
+  static void AddFilesToDir(const std::string& dir, const std::vector<std::string>& files) {
+    std::string zeros(4096, 0);
+    for (const auto& file : files) {
+      std::string path = dir + "/" + file;
+      ASSERT_TRUE(android::base::WriteStringToFile(zeros, path));
+    }
+  }
+
+  void SetUp() override {
+    Paths::Get().set_cache_log_directory(mock_log_dir.path);
+  }
+
+  // A mock method to calculate the free space. It assumes the partition has a total size of 40960
+  // bytes and all files are 4096 bytes in size.
+  size_t MockFreeSpaceChecker(const std::string& dirname) {
+    std::vector<std::string> files = FindFilesInDir(dirname);
+    return PARTITION_SIZE - 4096 * files.size();
+  }
+
+  TemporaryDir mock_cache;
+  TemporaryDir mock_log_dir;
+};
+
+TEST_F(FreeCacheTest, FreeCacheSmoke) {
+  std::vector<std::string> files = { "file1", "file2", "file3" };
+  AddFilesToDir(mock_cache.path, files);
+  ASSERT_EQ(files, FindFilesInDir(mock_cache.path));
+  ASSERT_EQ(4096 * 7, MockFreeSpaceChecker(mock_cache.path));
+
+  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 9, mock_cache.path, [&](const std::string& dir) {
+    return this->MockFreeSpaceChecker(dir);
+  }));
+
+  ASSERT_EQ(std::vector<std::string>{ "file3" }, FindFilesInDir(mock_cache.path));
+  ASSERT_EQ(4096 * 9, MockFreeSpaceChecker(mock_cache.path));
+}
+
+TEST_F(FreeCacheTest, FreeCacheOpenFile) {
+  std::vector<std::string> files = { "file1", "file2" };
+  AddFilesToDir(mock_cache.path, files);
+  ASSERT_EQ(files, FindFilesInDir(mock_cache.path));
+  ASSERT_EQ(4096 * 8, MockFreeSpaceChecker(mock_cache.path));
+
+  std::string file1_path = mock_cache.path + "/file1"s;
+  android::base::unique_fd fd(open(file1_path.c_str(), O_RDONLY));
+
+  // file1 can't be deleted as it's opened by us.
+  ASSERT_FALSE(RemoveFilesInDirectory(4096 * 10, mock_cache.path, [&](const std::string& dir) {
+    return this->MockFreeSpaceChecker(dir);
+  }));
+
+  ASSERT_EQ(std::vector<std::string>{ "file1" }, FindFilesInDir(mock_cache.path));
+}
+
+TEST_F(FreeCacheTest, FreeCacheLogsSmoke) {
+  std::vector<std::string> log_files = { "last_log", "last_log.1", "last_kmsg.2", "last_log.5",
+                                         "last_log.10" };
+  AddFilesToDir(mock_log_dir.path, log_files);
+  ASSERT_EQ(4096 * 5, MockFreeSpaceChecker(mock_log_dir.path));
+
+  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 8, mock_log_dir.path, [&](const std::string& dir) {
+    return this->MockFreeSpaceChecker(dir);
+  }));
+
+  // Logs with a higher index will be deleted first
+  std::vector<std::string> expected = { "last_log", "last_log.1" };
+  ASSERT_EQ(expected, FindFilesInDir(mock_log_dir.path));
+  ASSERT_EQ(4096 * 8, MockFreeSpaceChecker(mock_log_dir.path));
+}
+
+TEST_F(FreeCacheTest, FreeCacheLogsStringComparison) {
+  std::vector<std::string> log_files = { "last_log.1", "last_kmsg.1", "last_log.not_number",
+                                         "last_kmsgrandom" };
+  AddFilesToDir(mock_log_dir.path, log_files);
+  ASSERT_EQ(4096 * 6, MockFreeSpaceChecker(mock_log_dir.path));
+
+  ASSERT_TRUE(RemoveFilesInDirectory(4096 * 9, mock_log_dir.path, [&](const std::string& dir) {
+    return this->MockFreeSpaceChecker(dir);
+  }));
+
+  // Logs with incorrect format will be deleted first; and the last_kmsg with the same index is
+  // deleted before last_log.
+  std::vector<std::string> expected = { "last_log.1" };
+  ASSERT_EQ(expected, FindFilesInDir(mock_log_dir.path));
+  ASSERT_EQ(4096 * 9, MockFreeSpaceChecker(mock_log_dir.path));
+}
+
+TEST_F(FreeCacheTest, FreeCacheLogsOtherFiles) {
+  std::vector<std::string> log_files = { "last_install", "command", "block.map", "last_log",
+                                         "last_kmsg.1" };
+  AddFilesToDir(mock_log_dir.path, log_files);
+  ASSERT_EQ(4096 * 5, MockFreeSpaceChecker(mock_log_dir.path));
+
+  ASSERT_FALSE(RemoveFilesInDirectory(4096 * 8, mock_log_dir.path, [&](const std::string& dir) {
+    return this->MockFreeSpaceChecker(dir);
+  }));
+
+  // Non log files in /cache/recovery won't be deleted.
+  std::vector<std::string> expected = { "block.map", "command", "last_install" };
+  ASSERT_EQ(expected, FindFilesInDir(mock_log_dir.path));
+}