diff --git a/networksecurity/tests/unit/Android.bp b/networksecurity/tests/unit/Android.bp
new file mode 100644
index 0000000..639f644
--- /dev/null
+++ b/networksecurity/tests/unit/Android.bp
@@ -0,0 +1,44 @@
+// Copyright (C) 2024 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.
+package {
+    default_team: "trendy_team_platform_security",
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+android_test {
+    name: "NetworkSecurityUnitTests",
+    defaults: ["mts-target-sdk-version-current"],
+    test_suites: [
+        "general-tests",
+        "mts-tethering",
+    ],
+
+    srcs: ["src/**/*.java"],
+
+    libs: [
+        "android.test.base",
+        "android.test.mock",
+        "android.test.runner",
+    ],
+    static_libs: [
+        "androidx.test.ext.junit",
+        "androidx.test.rules",
+        "junit",
+        "mockito-target-minus-junit4",
+        "service-networksecurity-pre-jarjar",
+        "truth",
+    ],
+
+    sdk_version: "test_current",
+}
diff --git a/networksecurity/tests/unit/AndroidManifest.xml b/networksecurity/tests/unit/AndroidManifest.xml
new file mode 100644
index 0000000..7a3f4b7
--- /dev/null
+++ b/networksecurity/tests/unit/AndroidManifest.xml
@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2024 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.
+  -->
+
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+          package="com.android.net.ct">
+
+    <application>
+        <uses-library android:name="android.test.runner" />
+    </application>
+
+    <instrumentation
+        android:name="androidx.test.runner.AndroidJUnitRunner"
+        android:targetPackage="com.android.net.ct"
+        android:label="NetworkSecurity Mainline Module Tests" />
+</manifest>
diff --git a/networksecurity/tests/unit/AndroidTest.xml b/networksecurity/tests/unit/AndroidTest.xml
new file mode 100644
index 0000000..3c94df7
--- /dev/null
+++ b/networksecurity/tests/unit/AndroidTest.xml
@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ 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.
+  -->
+<configuration description="Runs NetworkSecurity Mainline unit Tests.">
+    <option name="test-tag" value="NetworkSecurityUnitTests" />
+
+    <target_preparer class="com.android.tradefed.targetprep.suite.SuiteApkInstaller">
+        <option name="test-file-name" value="NetworkSecurityUnitTests.apk" />
+    </target_preparer>
+
+    <option name="config-descriptor:metadata" key="mainline-param"
+            value="com.google.android.tethering.next.apex" />
+    <test class="com.android.tradefed.testtype.AndroidJUnitTest" >
+        <option name="package" value="com.android.net.ct" />
+        <option name="runner" value="androidx.test.runner.AndroidJUnitRunner" />
+    </test>
+
+    <!-- Only run in MTS if the Tethering Mainline module is installed. -->
+    <object type="module_controller"
+            class="com.android.tradefed.testtype.suite.module.MainlineTestModuleController">
+        <option name="mainline-module-package-name" value="com.google.android.tethering" />
+    </object>
+</configuration>
diff --git a/networksecurity/tests/unit/src/com/android/server/net/ct/CertificateTransparencyDownloaderTest.java b/networksecurity/tests/unit/src/com/android/server/net/ct/CertificateTransparencyDownloaderTest.java
new file mode 100644
index 0000000..acd0d36
--- /dev/null
+++ b/networksecurity/tests/unit/src/com/android/server/net/ct/CertificateTransparencyDownloaderTest.java
@@ -0,0 +1,145 @@
+/*
+ * Copyright (C) 2024 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.
+ */
+package com.android.server.net.ct;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import android.app.DownloadManager;
+import android.content.Context;
+import android.content.Intent;
+
+import androidx.test.platform.app.InstrumentationRegistry;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import java.io.File;
+import java.io.IOException;
+
+/** Tests for the {@link CertificateTransparencyDownloader}. */
+@RunWith(JUnit4.class)
+public class CertificateTransparencyDownloaderTest {
+
+    @Mock private DownloadHelper mDownloadHelper;
+
+    private Context mContext;
+    private File mTempFile;
+    private DataStore mDataStore;
+    private CertificateTransparencyDownloader mCertificateTransparencyDownloader;
+
+    @Before
+    public void setUp() throws IOException {
+        MockitoAnnotations.initMocks(this);
+
+        mContext = InstrumentationRegistry.getInstrumentation().getContext();
+        mTempFile = File.createTempFile("datastore-test", ".properties");
+        mDataStore = new DataStore(mTempFile);
+        mDataStore.load();
+
+        mCertificateTransparencyDownloader =
+                new CertificateTransparencyDownloader(mContext, mDataStore, mDownloadHelper);
+    }
+
+    @After
+    public void tearDown() {
+        mTempFile.delete();
+    }
+
+    @Test
+    public void testDownloader_startMetadataDownload() {
+        String metadataUrl = "http://test-metadata.org";
+        long downloadId = 666;
+        when(mDownloadHelper.startDownload(metadataUrl)).thenReturn(downloadId);
+
+        assertThat(mCertificateTransparencyDownloader.isMetadataDownloadId(downloadId)).isFalse();
+        mCertificateTransparencyDownloader.startMetadataDownload(metadataUrl);
+        assertThat(mCertificateTransparencyDownloader.isMetadataDownloadId(downloadId)).isTrue();
+    }
+
+    @Test
+    public void testDownloader_startContentDownload() {
+        String contentUrl = "http://test-content.org";
+        long downloadId = 666;
+        when(mDownloadHelper.startDownload(contentUrl)).thenReturn(downloadId);
+
+        assertThat(mCertificateTransparencyDownloader.isContentDownloadId(downloadId)).isFalse();
+        mCertificateTransparencyDownloader.startContentDownload(contentUrl);
+        assertThat(mCertificateTransparencyDownloader.isContentDownloadId(downloadId)).isTrue();
+    }
+
+    @Test
+    public void testDownloader_handleMetadataCompleteSuccessful() {
+        long metadataId = 123;
+        mDataStore.setPropertyLong(Config.METADATA_URL_KEY, metadataId);
+        when(mDownloadHelper.isSuccessful(metadataId)).thenReturn(true);
+
+        long contentId = 666;
+        String contentUrl = "http://test-content.org";
+        mDataStore.setProperty(Config.CONTENT_URL, contentUrl);
+        when(mDownloadHelper.startDownload(contentUrl)).thenReturn(contentId);
+
+        mCertificateTransparencyDownloader.onReceive(
+                mContext, makeDownloadCompleteIntent(metadataId));
+
+        assertThat(mCertificateTransparencyDownloader.isContentDownloadId(contentId)).isTrue();
+    }
+
+    @Test
+    public void testDownloader_handleMetadataCompleteFailed() {
+        long metadataId = 123;
+        mDataStore.setPropertyLong(Config.METADATA_URL_KEY, metadataId);
+        when(mDownloadHelper.isSuccessful(metadataId)).thenReturn(false);
+
+        String contentUrl = "http://test-content.org";
+        mDataStore.setProperty(Config.CONTENT_URL, contentUrl);
+
+        mCertificateTransparencyDownloader.onReceive(
+                mContext, makeDownloadCompleteIntent(metadataId));
+
+        verify(mDownloadHelper, never()).startDownload(contentUrl);
+    }
+
+    @Test
+    public void testDownloader_handleContentCompleteSuccessful() {
+        long metadataId = 123;
+        mDataStore.setPropertyLong(Config.METADATA_URL_KEY, metadataId);
+
+        long contentId = 666;
+        mDataStore.setPropertyLong(Config.CONTENT_URL_KEY, contentId);
+        when(mDownloadHelper.isSuccessful(contentId)).thenReturn(true);
+
+        mCertificateTransparencyDownloader.onReceive(
+                mContext, makeDownloadCompleteIntent(contentId));
+
+        verify(mDownloadHelper, times(1)).getUri(metadataId);
+        verify(mDownloadHelper, times(1)).getUri(contentId);
+    }
+
+    private Intent makeDownloadCompleteIntent(long downloadId) {
+        return new Intent(DownloadManager.ACTION_DOWNLOAD_COMPLETE)
+                .putExtra(DownloadManager.EXTRA_DOWNLOAD_ID, downloadId);
+    }
+}
diff --git a/networksecurity/tests/unit/src/com/android/server/net/ct/DataStoreTest.java b/networksecurity/tests/unit/src/com/android/server/net/ct/DataStoreTest.java
new file mode 100644
index 0000000..d16f138
--- /dev/null
+++ b/networksecurity/tests/unit/src/com/android/server/net/ct/DataStoreTest.java
@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2024 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.
+ */
+package com.android.server.net.ct;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import java.io.File;
+import java.io.IOException;
+
+/** Tests for the {@link DataStore}. */
+@RunWith(JUnit4.class)
+public class DataStoreTest {
+
+    private File mTempFile;
+    private DataStore mDataStore;
+
+    @Before
+    public void setUp() throws IOException {
+        mTempFile = File.createTempFile("datastore-test", ".properties");
+        mDataStore = new DataStore(mTempFile);
+        mDataStore.load();
+    }
+
+    @After
+    public void tearDown() {
+        mTempFile.delete();
+    }
+
+    @Test
+    public void testDataStore_propertyFileCreatedSuccessfully() {
+        assertThat(mTempFile.exists()).isTrue();
+        assertThat(mDataStore.isEmpty()).isTrue();
+    }
+
+    @Test
+    public void testDataStore_propertySet() {
+        String stringProperty = "prop1";
+        String stringValue = "i_am_a_string";
+        String longProperty = "prop3";
+        long longValue = 9000;
+
+        assertThat(mDataStore.getProperty(stringProperty)).isNull();
+        assertThat(mDataStore.getPropertyLong(longProperty, -1)).isEqualTo(-1);
+
+        mDataStore.setProperty(stringProperty, stringValue);
+        mDataStore.setPropertyLong(longProperty, longValue);
+
+        assertThat(mDataStore.getProperty(stringProperty)).isEqualTo(stringValue);
+        assertThat(mDataStore.getPropertyLong(longProperty, -1)).isEqualTo(longValue);
+    }
+
+    @Test
+    public void testDataStore_propertyStore() {
+        String stringProperty = "prop1";
+        String stringValue = "i_am_a_string";
+        String longProperty = "prop3";
+        long longValue = 9000;
+
+        mDataStore.setProperty(stringProperty, stringValue);
+        mDataStore.setPropertyLong(longProperty, longValue);
+        mDataStore.store();
+
+        mDataStore.clear();
+        assertThat(mDataStore.getProperty(stringProperty)).isNull();
+        assertThat(mDataStore.getPropertyLong(longProperty, -1)).isEqualTo(-1);
+
+        mDataStore.load();
+        assertThat(mDataStore.getProperty(stringProperty)).isEqualTo(stringValue);
+        assertThat(mDataStore.getPropertyLong(longProperty, -1)).isEqualTo(longValue);
+    }
+}
diff --git a/networksecurity/tests/unit/src/com/android/server/net/ct/DownloadHelperTest.java b/networksecurity/tests/unit/src/com/android/server/net/ct/DownloadHelperTest.java
new file mode 100644
index 0000000..0b65e3c
--- /dev/null
+++ b/networksecurity/tests/unit/src/com/android/server/net/ct/DownloadHelperTest.java
@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2024 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.
+ */
+package com.android.server.net.ct;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import static org.junit.Assert.assertThrows;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.when;
+
+import android.app.DownloadManager;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+/** Tests for the {@link DownloadHelper}. */
+@RunWith(JUnit4.class)
+public class DownloadHelperTest {
+
+    @Mock private DownloadManager mDownloadManager;
+
+    private DownloadHelper mDownloadHelper;
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+
+        mDownloadHelper = new DownloadHelper(mDownloadManager);
+    }
+
+    @Test
+    public void testDownloadHelper_scheduleDownload() {
+        long downloadId = 666;
+        when(mDownloadManager.enqueue(any())).thenReturn(downloadId);
+
+        assertThat(mDownloadHelper.startDownload("http://test.org")).isEqualTo(downloadId);
+    }
+
+    @Test
+    public void testDownloadHelper_wrongUri() {
+        when(mDownloadManager.enqueue(any())).thenReturn(666L);
+
+        assertThrows(
+                IllegalArgumentException.class, () -> mDownloadHelper.startDownload("not_a_uri"));
+    }
+}