diff --git a/Tethering/src/com/android/networkstack/tethering/OffloadHardwareInterface.java b/Tethering/src/com/android/networkstack/tethering/OffloadHardwareInterface.java
index 293f8ea..fe92204 100644
--- a/Tethering/src/com/android/networkstack/tethering/OffloadHardwareInterface.java
+++ b/Tethering/src/com/android/networkstack/tethering/OffloadHardwareInterface.java
@@ -66,6 +66,7 @@
 
     private final Handler mHandler;
     private final SharedLog mLog;
+    private final Dependencies mDeps;
     private IOffloadControl mOffloadControl;
     private TetheringOffloadCallback mTetheringOffloadCallback;
     private ControlCallback mControlCallback;
@@ -126,8 +127,76 @@
     }
 
     public OffloadHardwareInterface(Handler h, SharedLog log) {
+        this(h, log, new Dependencies(log));
+    }
+
+    OffloadHardwareInterface(Handler h, SharedLog log, Dependencies deps) {
         mHandler = h;
         mLog = log.forSubComponent(TAG);
+        mDeps = deps;
+    }
+
+    /** Capture OffloadHardwareInterface dependencies, for injection. */
+    static class Dependencies {
+        private final SharedLog mLog;
+
+        Dependencies(SharedLog log) {
+            mLog = log;
+        }
+
+        public IOffloadConfig getOffloadConfig() {
+            try {
+                return IOffloadConfig.getService(true /*retry*/);
+            } catch (RemoteException | NoSuchElementException e) {
+                mLog.e("getIOffloadConfig error " + e);
+                return null;
+            }
+        }
+
+        public IOffloadControl getOffloadControl() {
+            try {
+                return IOffloadControl.getService(true /*retry*/);
+            } catch (RemoteException | NoSuchElementException e) {
+                mLog.e("tethering offload control not supported: " + e);
+                return null;
+            }
+        }
+
+        public NativeHandle createConntrackSocket(final int groups) {
+            final FileDescriptor fd;
+            try {
+                fd = NetlinkSocket.forProto(OsConstants.NETLINK_NETFILTER);
+            } catch (ErrnoException e) {
+                mLog.e("Unable to create conntrack socket " + e);
+                return null;
+            }
+
+            final SocketAddress sockAddr = SocketUtils.makeNetlinkSocketAddress(0, groups);
+            try {
+                Os.bind(fd, sockAddr);
+            } catch (ErrnoException | SocketException e) {
+                mLog.e("Unable to bind conntrack socket for groups " + groups + " error: " + e);
+                try {
+                    SocketUtils.closeSocket(fd);
+                } catch (IOException ie) {
+                    // Nothing we can do here
+                }
+                return null;
+            }
+            try {
+                Os.connect(fd, sockAddr);
+            } catch (ErrnoException | SocketException e) {
+                mLog.e("connect to kernel fail for groups " + groups + " error: " + e);
+                try {
+                    SocketUtils.closeSocket(fd);
+                } catch (IOException ie) {
+                    // Nothing we can do here
+                }
+                return null;
+            }
+
+            return new NativeHandle(fd, true);
+        }
     }
 
     /** Get default value indicating whether offload is supported. */
@@ -141,13 +210,7 @@
      * share them with offload management process.
      */
     public boolean initOffloadConfig() {
-        IOffloadConfig offloadConfig;
-        try {
-            offloadConfig = IOffloadConfig.getService(true /*retry*/);
-        } catch (RemoteException | NoSuchElementException e) {
-            mLog.e("getIOffloadConfig error " + e);
-            return false;
-        }
+        final IOffloadConfig offloadConfig = mDeps.getOffloadConfig();
         if (offloadConfig == null) {
             mLog.e("Could not find IOffloadConfig service");
             return false;
@@ -159,11 +222,11 @@
         //
         // h2    provides a file descriptor bound to the following netlink groups
         //       (NF_NETLINK_CONNTRACK_UPDATE | NF_NETLINK_CONNTRACK_DESTROY).
-        final NativeHandle h1 = createConntrackSocket(
+        final NativeHandle h1 = mDeps.createConntrackSocket(
                 NF_NETLINK_CONNTRACK_NEW | NF_NETLINK_CONNTRACK_DESTROY);
         if (h1 == null) return false;
 
-        final NativeHandle h2 = createConntrackSocket(
+        final NativeHandle h2 = mDeps.createConntrackSocket(
                 NF_NETLINK_CONNTRACK_UPDATE | NF_NETLINK_CONNTRACK_DESTROY);
         if (h2 == null) {
             closeFdInNativeHandle(h1);
@@ -198,53 +261,12 @@
         }
     }
 
-    private NativeHandle createConntrackSocket(final int groups) {
-        FileDescriptor fd;
-        try {
-            fd = NetlinkSocket.forProto(OsConstants.NETLINK_NETFILTER);
-        } catch (ErrnoException e) {
-            mLog.e("Unable to create conntrack socket " + e);
-            return null;
-        }
-
-        final SocketAddress sockAddr = SocketUtils.makeNetlinkSocketAddress(0, groups);
-        try {
-            Os.bind(fd, sockAddr);
-        } catch (ErrnoException | SocketException e) {
-            mLog.e("Unable to bind conntrack socket for groups " + groups + " error: " + e);
-            try {
-                SocketUtils.closeSocket(fd);
-            } catch (IOException ie) {
-                // Nothing we can do here
-            }
-            return null;
-        }
-        try {
-            Os.connect(fd, sockAddr);
-        } catch (ErrnoException | SocketException e) {
-            mLog.e("connect to kernel fail for groups " + groups + " error: " + e);
-            try {
-                SocketUtils.closeSocket(fd);
-            } catch (IOException ie) {
-                // Nothing we can do here
-            }
-            return null;
-        }
-
-        return new NativeHandle(fd, true);
-    }
-
     /** Initialize the tethering offload HAL. */
     public boolean initOffloadControl(ControlCallback controlCb) {
         mControlCallback = controlCb;
 
         if (mOffloadControl == null) {
-            try {
-                mOffloadControl = IOffloadControl.getService(true /*retry*/);
-            } catch (RemoteException | NoSuchElementException e) {
-                mLog.e("tethering offload control not supported: " + e);
-                return false;
-            }
+            mOffloadControl = mDeps.getOffloadControl();
             if (mOffloadControl == null) {
                 mLog.e("tethering IOffloadControl.getService() returned null");
                 return false;
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/OffloadHardwareInterfaceTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/OffloadHardwareInterfaceTest.java
new file mode 100644
index 0000000..f8ff1cb
--- /dev/null
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/OffloadHardwareInterfaceTest.java
@@ -0,0 +1,215 @@
+/*
+ * Copyright (C) 2020 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.networkstack.tethering;
+
+import static android.net.util.TetheringUtils.uint16;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+
+import android.hardware.tetheroffload.config.V1_0.IOffloadConfig;
+import android.hardware.tetheroffload.control.V1_0.IOffloadControl;
+import android.hardware.tetheroffload.control.V1_0.ITetheringOffloadCallback;
+import android.hardware.tetheroffload.control.V1_0.NatTimeoutUpdate;
+import android.hardware.tetheroffload.control.V1_0.NetworkProtocol;
+import android.hardware.tetheroffload.control.V1_0.OffloadCallbackEvent;
+import android.net.util.SharedLog;
+import android.os.Handler;
+import android.os.NativeHandle;
+import android.os.test.TestLooper;
+import android.system.OsConstants;
+
+import androidx.test.filters.SmallTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import java.util.ArrayList;
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public final class OffloadHardwareInterfaceTest {
+    private static final String RMNET0 = "test_rmnet_data0";
+
+    private final TestLooper mTestLooper = new TestLooper();
+
+    private OffloadHardwareInterface mOffloadHw;
+    private ITetheringOffloadCallback mTetheringOffloadCallback;
+    private OffloadHardwareInterface.ControlCallback mControlCallback;
+
+    @Mock private IOffloadConfig mIOffloadConfig;
+    @Mock private IOffloadControl mIOffloadControl;
+    @Mock private NativeHandle mNativeHandle;
+
+    class MyDependencies extends OffloadHardwareInterface.Dependencies {
+        MyDependencies(SharedLog log) {
+            super(log);
+        }
+
+        @Override
+        public IOffloadConfig getOffloadConfig() {
+            return mIOffloadConfig;
+        }
+
+        @Override
+        public IOffloadControl getOffloadControl() {
+            return mIOffloadControl;
+        }
+
+        @Override
+        public NativeHandle createConntrackSocket(final int groups) {
+            return mNativeHandle;
+        }
+    }
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+        final SharedLog log = new SharedLog("test");
+        mOffloadHw = new OffloadHardwareInterface(new Handler(mTestLooper.getLooper()), log,
+                new MyDependencies(log));
+        mControlCallback = spy(new OffloadHardwareInterface.ControlCallback());
+    }
+
+    private void startOffloadHardwareInterface() throws Exception {
+        mOffloadHw.initOffloadConfig();
+        mOffloadHw.initOffloadControl(mControlCallback);
+        final ArgumentCaptor<ITetheringOffloadCallback> mOffloadCallbackCaptor =
+                ArgumentCaptor.forClass(ITetheringOffloadCallback.class);
+        verify(mIOffloadControl).initOffload(mOffloadCallbackCaptor.capture(), any());
+        mTetheringOffloadCallback = mOffloadCallbackCaptor.getValue();
+    }
+
+    @Test
+    public void testGetForwardedStats() throws Exception {
+        startOffloadHardwareInterface();
+        final OffloadHardwareInterface.ForwardedStats stats = mOffloadHw.getForwardedStats(RMNET0);
+        verify(mIOffloadControl).getForwardedStats(eq(RMNET0), any());
+        assertNotNull(stats);
+    }
+
+    @Test
+    public void testSetLocalPrefixes() throws Exception {
+        startOffloadHardwareInterface();
+        final ArrayList<String> localPrefixes = new ArrayList<>();
+        localPrefixes.add("127.0.0.0/8");
+        localPrefixes.add("fe80::/64");
+        mOffloadHw.setLocalPrefixes(localPrefixes);
+        verify(mIOffloadControl).setLocalPrefixes(eq(localPrefixes), any());
+    }
+
+    @Test
+    public void testSetDataLimit() throws Exception {
+        startOffloadHardwareInterface();
+        final long limit = 12345;
+        mOffloadHw.setDataLimit(RMNET0, limit);
+        verify(mIOffloadControl).setDataLimit(eq(RMNET0), eq(limit), any());
+    }
+
+    @Test
+    public void testSetUpstreamParameters() throws Exception {
+        startOffloadHardwareInterface();
+        final String v4addr = "192.168.10.1";
+        final String v4gateway = "192.168.10.255";
+        final ArrayList<String> v6gws = new ArrayList<>(0);
+        v6gws.add("2001:db8::1");
+        mOffloadHw.setUpstreamParameters(RMNET0, v4addr, v4gateway, v6gws);
+        verify(mIOffloadControl).setUpstreamParameters(eq(RMNET0), eq(v4addr), eq(v4gateway),
+                eq(v6gws), any());
+
+        final ArgumentCaptor<ArrayList<String>> mArrayListCaptor =
+                ArgumentCaptor.forClass(ArrayList.class);
+        mOffloadHw.setUpstreamParameters(null, null, null, null);
+        verify(mIOffloadControl).setUpstreamParameters(eq(""), eq(""), eq(""),
+                mArrayListCaptor.capture(), any());
+        assertEquals(mArrayListCaptor.getValue().size(), 0);
+    }
+
+    @Test
+    public void testUpdateDownstreamPrefix() throws Exception {
+        startOffloadHardwareInterface();
+        final String ifName = "wlan1";
+        final String prefix = "192.168.43.0/24";
+        mOffloadHw.addDownstreamPrefix(ifName, prefix);
+        verify(mIOffloadControl).addDownstream(eq(ifName), eq(prefix), any());
+
+        mOffloadHw.removeDownstreamPrefix(ifName, prefix);
+        verify(mIOffloadControl).removeDownstream(eq(ifName), eq(prefix), any());
+    }
+
+    @Test
+    public void testTetheringOffloadCallback() throws Exception {
+        startOffloadHardwareInterface();
+
+        mTetheringOffloadCallback.onEvent(OffloadCallbackEvent.OFFLOAD_STARTED);
+        mTestLooper.dispatchAll();
+        verify(mControlCallback).onStarted();
+
+        mTetheringOffloadCallback.onEvent(OffloadCallbackEvent.OFFLOAD_STOPPED_ERROR);
+        mTestLooper.dispatchAll();
+        verify(mControlCallback).onStoppedError();
+
+        mTetheringOffloadCallback.onEvent(OffloadCallbackEvent.OFFLOAD_STOPPED_UNSUPPORTED);
+        mTestLooper.dispatchAll();
+        verify(mControlCallback).onStoppedUnsupported();
+
+        mTetheringOffloadCallback.onEvent(OffloadCallbackEvent.OFFLOAD_SUPPORT_AVAILABLE);
+        mTestLooper.dispatchAll();
+        verify(mControlCallback).onSupportAvailable();
+
+        mTetheringOffloadCallback.onEvent(OffloadCallbackEvent.OFFLOAD_STOPPED_LIMIT_REACHED);
+        mTestLooper.dispatchAll();
+        verify(mControlCallback).onStoppedLimitReached();
+
+        final NatTimeoutUpdate tcpParams = buildNatTimeoutUpdate(NetworkProtocol.TCP);
+        mTetheringOffloadCallback.updateTimeout(tcpParams);
+        mTestLooper.dispatchAll();
+        verify(mControlCallback).onNatTimeoutUpdate(eq(OsConstants.IPPROTO_TCP),
+                eq(tcpParams.src.addr),
+                eq(uint16(tcpParams.src.port)),
+                eq(tcpParams.dst.addr),
+                eq(uint16(tcpParams.dst.port)));
+
+        final NatTimeoutUpdate udpParams = buildNatTimeoutUpdate(NetworkProtocol.UDP);
+        mTetheringOffloadCallback.updateTimeout(udpParams);
+        mTestLooper.dispatchAll();
+        verify(mControlCallback).onNatTimeoutUpdate(eq(OsConstants.IPPROTO_UDP),
+                eq(udpParams.src.addr),
+                eq(uint16(udpParams.src.port)),
+                eq(udpParams.dst.addr),
+                eq(uint16(udpParams.dst.port)));
+    }
+
+    private NatTimeoutUpdate buildNatTimeoutUpdate(final int proto) {
+        final NatTimeoutUpdate params = new NatTimeoutUpdate();
+        params.proto = proto;
+        params.src.addr = "192.168.43.200";
+        params.src.port = 100;
+        params.dst.addr = "172.50.46.169";
+        params.dst.port = 150;
+        return params;
+    }
+}