diff --git a/netd/BpfHandlerTest.cpp b/netd/BpfHandlerTest.cpp
new file mode 100644
index 0000000..db59c7c
--- /dev/null
+++ b/netd/BpfHandlerTest.cpp
@@ -0,0 +1,244 @@
+/*
+ * Copyright 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.
+ *
+ * BpfHandlerTest.cpp - unit tests for BpfHandler.cpp
+ */
+
+#include <sys/socket.h>
+
+#include <gtest/gtest.h>
+
+#include "BpfHandler.h"
+
+using namespace android::bpf;  // NOLINT(google-build-using-namespace): exempted
+
+namespace android {
+namespace net {
+
+using base::Result;
+
+constexpr int TEST_MAP_SIZE = 10;
+constexpr int TEST_COOKIE = 1;
+constexpr uid_t TEST_UID = 10086;
+constexpr uid_t TEST_UID2 = 54321;
+constexpr uint32_t TEST_TAG = 42;
+constexpr uint32_t TEST_COUNTERSET = 1;
+constexpr uint32_t TEST_PER_UID_STATS_ENTRIES_LIMIT = 3;
+constexpr uint32_t TEST_TOTAL_UID_STATS_ENTRIES_LIMIT = 7;
+
+#define ASSERT_VALID(x) ASSERT_TRUE((x).isValid())
+
+class BpfHandlerTest : public ::testing::Test {
+  protected:
+    BpfHandlerTest()
+        : mBh(TEST_PER_UID_STATS_ENTRIES_LIMIT, TEST_TOTAL_UID_STATS_ENTRIES_LIMIT) {}
+    BpfHandler mBh;
+    BpfMap<uint64_t, UidTagValue> mFakeCookieTagMap;
+    BpfMap<StatsKey, StatsValue> mFakeStatsMapA;
+    BpfMap<uint32_t, uint8_t> mFakeConfigurationMap;
+    BpfMap<uint32_t, uint8_t> mFakeUidPermissionMap;
+
+    void SetUp() {
+        std::lock_guard guard(mBh.mMutex);
+        ASSERT_EQ(0, setrlimitForTest());
+
+        mFakeCookieTagMap.reset(createMap(BPF_MAP_TYPE_HASH, sizeof(uint64_t), sizeof(UidTagValue),
+                                          TEST_MAP_SIZE, 0));
+        ASSERT_VALID(mFakeCookieTagMap);
+
+        mFakeStatsMapA.reset(createMap(BPF_MAP_TYPE_HASH, sizeof(StatsKey), sizeof(StatsValue),
+                                       TEST_MAP_SIZE, 0));
+        ASSERT_VALID(mFakeStatsMapA);
+
+        mFakeConfigurationMap.reset(
+                createMap(BPF_MAP_TYPE_HASH, sizeof(uint32_t), sizeof(uint8_t), 1, 0));
+        ASSERT_VALID(mFakeConfigurationMap);
+
+        mFakeUidPermissionMap.reset(
+                createMap(BPF_MAP_TYPE_HASH, sizeof(uint32_t), sizeof(uint8_t), TEST_MAP_SIZE, 0));
+        ASSERT_VALID(mFakeUidPermissionMap);
+
+        mBh.mCookieTagMap.reset(dupFd(mFakeCookieTagMap.getMap()));
+        ASSERT_VALID(mBh.mCookieTagMap);
+        mBh.mStatsMapA.reset(dupFd(mFakeStatsMapA.getMap()));
+        ASSERT_VALID(mBh.mStatsMapA);
+        mBh.mConfigurationMap.reset(dupFd(mFakeConfigurationMap.getMap()));
+        ASSERT_VALID(mBh.mConfigurationMap);
+        // Always write to stats map A by default.
+        ASSERT_RESULT_OK(mBh.mConfigurationMap.writeValue(CURRENT_STATS_MAP_CONFIGURATION_KEY,
+                                                          SELECT_MAP_A, BPF_ANY));
+        mBh.mUidPermissionMap.reset(dupFd(mFakeUidPermissionMap.getMap()));
+        ASSERT_VALID(mBh.mUidPermissionMap);
+    }
+
+    int dupFd(const android::base::unique_fd& mapFd) {
+        return fcntl(mapFd.get(), F_DUPFD_CLOEXEC, 0);
+    }
+
+    int setUpSocketAndTag(int protocol, uint64_t* cookie, uint32_t tag, uid_t uid,
+                          uid_t realUid) {
+        int sock = socket(protocol, SOCK_STREAM | SOCK_CLOEXEC, 0);
+        EXPECT_LE(0, sock);
+        *cookie = getSocketCookie(sock);
+        EXPECT_NE(NONEXISTENT_COOKIE, *cookie);
+        EXPECT_EQ(0, mBh.tagSocket(sock, tag, uid, realUid));
+        return sock;
+    }
+
+    void expectUidTag(uint64_t cookie, uid_t uid, uint32_t tag) {
+        Result<UidTagValue> tagResult = mFakeCookieTagMap.readValue(cookie);
+        ASSERT_RESULT_OK(tagResult);
+        EXPECT_EQ(uid, tagResult.value().uid);
+        EXPECT_EQ(tag, tagResult.value().tag);
+    }
+
+    void expectNoTag(uint64_t cookie) { EXPECT_FALSE(mFakeCookieTagMap.readValue(cookie).ok()); }
+
+    void populateFakeStats(uint64_t cookie, uint32_t uid, uint32_t tag, StatsKey* key) {
+        UidTagValue cookieMapkey = {.uid = (uint32_t)uid, .tag = tag};
+        EXPECT_RESULT_OK(mFakeCookieTagMap.writeValue(cookie, cookieMapkey, BPF_ANY));
+        *key = {.uid = uid, .tag = tag, .counterSet = TEST_COUNTERSET, .ifaceIndex = 1};
+        StatsValue statsMapValue = {.rxPackets = 1, .rxBytes = 100};
+        EXPECT_RESULT_OK(mFakeStatsMapA.writeValue(*key, statsMapValue, BPF_ANY));
+        key->tag = 0;
+        EXPECT_RESULT_OK(mFakeStatsMapA.writeValue(*key, statsMapValue, BPF_ANY));
+        // put tag information back to statsKey
+        key->tag = tag;
+    }
+
+    template <class Key, class Value>
+    void expectMapEmpty(BpfMap<Key, Value>& map) {
+        auto isEmpty = map.isEmpty();
+        EXPECT_RESULT_OK(isEmpty);
+        EXPECT_TRUE(isEmpty.value());
+    }
+
+    void expectTagSocketReachLimit(uint32_t tag, uint32_t uid) {
+        int sock = socket(AF_INET6, SOCK_STREAM | SOCK_CLOEXEC, 0);
+        EXPECT_LE(0, sock);
+        if (sock < 0) return;
+        uint64_t sockCookie = getSocketCookie(sock);
+        EXPECT_NE(NONEXISTENT_COOKIE, sockCookie);
+        EXPECT_EQ(-EMFILE, mBh.tagSocket(sock, tag, uid, uid));
+        expectNoTag(sockCookie);
+
+        // Delete stats entries then tag socket success
+        StatsKey key = {.uid = uid, .tag = 0, .counterSet = TEST_COUNTERSET, .ifaceIndex = 1};
+        ASSERT_RESULT_OK(mFakeStatsMapA.deleteValue(key));
+        EXPECT_EQ(0, mBh.tagSocket(sock, tag, uid, uid));
+        expectUidTag(sockCookie, uid, tag);
+    }
+};
+
+TEST_F(BpfHandlerTest, TestTagSocketV4) {
+    uint64_t sockCookie;
+    int v4socket = setUpSocketAndTag(AF_INET, &sockCookie, TEST_TAG, TEST_UID, TEST_UID);
+    expectUidTag(sockCookie, TEST_UID, TEST_TAG);
+    ASSERT_EQ(0, mBh.untagSocket(v4socket));
+    expectNoTag(sockCookie);
+    expectMapEmpty(mFakeCookieTagMap);
+}
+
+TEST_F(BpfHandlerTest, TestReTagSocket) {
+    uint64_t sockCookie;
+    int v4socket = setUpSocketAndTag(AF_INET, &sockCookie, TEST_TAG, TEST_UID, TEST_UID);
+    expectUidTag(sockCookie, TEST_UID, TEST_TAG);
+    ASSERT_EQ(0, mBh.tagSocket(v4socket, TEST_TAG + 1, TEST_UID + 1, TEST_UID + 1));
+    expectUidTag(sockCookie, TEST_UID + 1, TEST_TAG + 1);
+}
+
+TEST_F(BpfHandlerTest, TestTagTwoSockets) {
+    uint64_t sockCookie1;
+    uint64_t sockCookie2;
+    int v4socket1 = setUpSocketAndTag(AF_INET, &sockCookie1, TEST_TAG, TEST_UID, TEST_UID);
+    setUpSocketAndTag(AF_INET, &sockCookie2, TEST_TAG, TEST_UID, TEST_UID);
+    expectUidTag(sockCookie1, TEST_UID, TEST_TAG);
+    expectUidTag(sockCookie2, TEST_UID, TEST_TAG);
+    ASSERT_EQ(0, mBh.untagSocket(v4socket1));
+    expectNoTag(sockCookie1);
+    expectUidTag(sockCookie2, TEST_UID, TEST_TAG);
+    ASSERT_FALSE(mFakeCookieTagMap.getNextKey(sockCookie2).ok());
+}
+
+TEST_F(BpfHandlerTest, TestTagSocketV6) {
+    uint64_t sockCookie;
+    int v6socket = setUpSocketAndTag(AF_INET6, &sockCookie, TEST_TAG, TEST_UID, TEST_UID);
+    expectUidTag(sockCookie, TEST_UID, TEST_TAG);
+    ASSERT_EQ(0, mBh.untagSocket(v6socket));
+    expectNoTag(sockCookie);
+    expectMapEmpty(mFakeCookieTagMap);
+}
+
+TEST_F(BpfHandlerTest, TestTagInvalidSocket) {
+    int invalidSocket = -1;
+    ASSERT_GT(0, mBh.tagSocket(invalidSocket, TEST_TAG, TEST_UID, TEST_UID));
+    expectMapEmpty(mFakeCookieTagMap);
+}
+
+TEST_F(BpfHandlerTest, TestTagSocketWithoutPermission) {
+    int sock = socket(AF_INET6, SOCK_STREAM | SOCK_CLOEXEC, 0);
+    ASSERT_NE(-1, sock);
+    ASSERT_EQ(-EPERM, mBh.tagSocket(sock, TEST_TAG, TEST_UID, TEST_UID2));
+    expectMapEmpty(mFakeCookieTagMap);
+}
+
+TEST_F(BpfHandlerTest, TestTagSocketWithPermission) {
+    // Grant permission to real uid. In practice, the uid permission map will be updated by
+    // TrafficController::setPermissionForUids().
+    uid_t realUid = TEST_UID2;
+    ASSERT_RESULT_OK(mFakeUidPermissionMap.writeValue(realUid,
+                     BPF_PERMISSION_UPDATE_DEVICE_STATS, BPF_ANY));
+
+    // Tag a socket to a different uid other then realUid.
+    uint64_t sockCookie;
+    int v6socket = setUpSocketAndTag(AF_INET6, &sockCookie, TEST_TAG, TEST_UID, realUid);
+    expectUidTag(sockCookie, TEST_UID, TEST_TAG);
+    EXPECT_EQ(0, mBh.untagSocket(v6socket));
+    expectNoTag(sockCookie);
+    expectMapEmpty(mFakeCookieTagMap);
+}
+
+TEST_F(BpfHandlerTest, TestUntagInvalidSocket) {
+    int invalidSocket = -1;
+    ASSERT_GT(0, mBh.untagSocket(invalidSocket));
+    int v4socket = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
+    ASSERT_GT(0, mBh.untagSocket(v4socket));
+    expectMapEmpty(mFakeCookieTagMap);
+}
+
+TEST_F(BpfHandlerTest, TestTagSocketReachLimitFail) {
+    uid_t uid = TEST_UID;
+    StatsKey tagStatsMapKey[3];
+    for (int i = 0; i < 3; i++) {
+        uint64_t cookie = TEST_COOKIE + i;
+        uint32_t tag = TEST_TAG + i;
+        populateFakeStats(cookie, uid, tag, &tagStatsMapKey[i]);
+    }
+    expectTagSocketReachLimit(TEST_TAG, TEST_UID);
+}
+
+TEST_F(BpfHandlerTest, TestTagSocketReachTotalLimitFail) {
+    StatsKey tagStatsMapKey[4];
+    for (int i = 0; i < 4; i++) {
+        uint64_t cookie = TEST_COOKIE + i;
+        uint32_t tag = TEST_TAG + i;
+        uid_t uid = TEST_UID + i;
+        populateFakeStats(cookie, uid, tag, &tagStatsMapKey[i]);
+    }
+    expectTagSocketReachLimit(TEST_TAG, TEST_UID);
+}
+
+}  // namespace net
+}  // namespace android