diff --git a/service/src/com/android/server/net/DelayedDiskWrite.java b/service/src/com/android/server/net/DelayedDiskWrite.java
index 35dc455..41cb419 100644
--- a/service/src/com/android/server/net/DelayedDiskWrite.java
+++ b/service/src/com/android/server/net/DelayedDiskWrite.java
@@ -21,6 +21,8 @@
 import android.text.TextUtils;
 import android.util.Log;
 
+import com.android.internal.annotations.VisibleForTesting;
+
 import java.io.BufferedOutputStream;
 import java.io.DataOutputStream;
 import java.io.FileOutputStream;
@@ -32,11 +34,42 @@
 public class DelayedDiskWrite {
     private static final String TAG = "DelayedDiskWrite";
 
+    private final Dependencies mDeps;
+
     private HandlerThread mDiskWriteHandlerThread;
     private Handler mDiskWriteHandler;
     /* Tracks multiple writes on the same thread */
     private int mWriteSequence = 0;
 
+    public DelayedDiskWrite() {
+        this(new Dependencies());
+    }
+
+    @VisibleForTesting
+    DelayedDiskWrite(Dependencies deps) {
+        mDeps = deps;
+    }
+
+    /**
+     * Dependencies class of DelayedDiskWrite, used for injection in tests.
+     */
+    @VisibleForTesting
+    static class Dependencies {
+        /**
+         * Create a HandlerThread to use in DelayedDiskWrite.
+         */
+        public HandlerThread makeHandlerThread() {
+            return new HandlerThread("DelayedDiskWriteThread");
+        }
+
+        /**
+         * Quit the HandlerThread looper.
+         */
+        public void quitHandlerThread(HandlerThread handlerThread) {
+            handlerThread.getLooper().quit();
+        }
+    }
+
     /**
      * Used to do a delayed data write to a given {@link OutputStream}.
      */
@@ -65,7 +98,7 @@
         /* Do a delayed write to disk on a separate handler thread */
         synchronized (this) {
             if (++mWriteSequence == 1) {
-                mDiskWriteHandlerThread = new HandlerThread("DelayedDiskWriteThread");
+                mDiskWriteHandlerThread = mDeps.makeHandlerThread();
                 mDiskWriteHandlerThread.start();
                 mDiskWriteHandler = new Handler(mDiskWriteHandlerThread.getLooper());
             }
@@ -99,9 +132,9 @@
             // Quit if no more writes sent
             synchronized (this) {
                 if (--mWriteSequence == 0) {
-                    mDiskWriteHandler.getLooper().quit();
-                    mDiskWriteHandler = null;
+                    mDeps.quitHandlerThread(mDiskWriteHandlerThread);
                     mDiskWriteHandlerThread = null;
+                    mDiskWriteHandler = null;
                 }
             }
         }
diff --git a/tests/unit/java/com/android/server/net/IpConfigStoreTest.java b/tests/unit/java/com/android/server/net/IpConfigStoreTest.java
index 1801c45..4adc999 100644
--- a/tests/unit/java/com/android/server/net/IpConfigStoreTest.java
+++ b/tests/unit/java/com/android/server/net/IpConfigStoreTest.java
@@ -20,6 +20,7 @@
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.fail;
 
+import android.content.Context;
 import android.net.InetAddresses;
 import android.net.IpConfiguration;
 import android.net.IpConfiguration.IpAssignment;
@@ -28,10 +29,14 @@
 import android.net.ProxyInfo;
 import android.net.StaticIpConfiguration;
 import android.os.Build;
+import android.os.HandlerThread;
 import android.util.ArrayMap;
 
+import androidx.test.InstrumentationRegistry;
+
 import com.android.testutils.DevSdkIgnoreRule;
 import com.android.testutils.DevSdkIgnoreRunner;
+import com.android.testutils.HandlerUtils;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -39,11 +44,13 @@
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.DataOutputStream;
+import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.InetAddress;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.List;
 
 /**
  * Unit tests for {@link IpConfigStore}
@@ -51,6 +58,7 @@
 @RunWith(DevSdkIgnoreRunner.class)
 @DevSdkIgnoreRule.IgnoreUpTo(Build.VERSION_CODES.S_V2)
 public class IpConfigStoreTest {
+    private static final int TIMEOUT_MS = 2_000;
     private static final int KEY_CONFIG = 17;
     private static final String IFACE_1 = "eth0";
     private static final String IFACE_2 = "eth1";
@@ -59,6 +67,22 @@
     private static final String DNS_IP_ADDR_1 = "1.2.3.4";
     private static final String DNS_IP_ADDR_2 = "5.6.7.8";
 
+    private static final ArrayList<InetAddress> DNS_SERVERS = new ArrayList<>(List.of(
+            InetAddresses.parseNumericAddress(DNS_IP_ADDR_1),
+            InetAddresses.parseNumericAddress(DNS_IP_ADDR_2)));
+    private static final StaticIpConfiguration STATIC_IP_CONFIG_1 =
+            new StaticIpConfiguration.Builder()
+                    .setIpAddress(new LinkAddress(IP_ADDR_1))
+                    .setDnsServers(DNS_SERVERS)
+                    .build();
+    private static final StaticIpConfiguration STATIC_IP_CONFIG_2 =
+            new StaticIpConfiguration.Builder()
+                    .setIpAddress(new LinkAddress(IP_ADDR_2))
+                    .setDnsServers(DNS_SERVERS)
+                    .build();
+    private static final ProxyInfo PROXY_INFO =
+            ProxyInfo.buildDirectProxy("10.10.10.10", 88, Arrays.asList("host1", "host2"));
+
     @Test
     public void backwardCompatibility2to3() throws IOException {
         ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
@@ -82,40 +106,73 @@
 
     @Test
     public void staticIpMultiNetworks() throws Exception {
-        final ArrayList<InetAddress> dnsServers = new ArrayList<>();
-        dnsServers.add(InetAddresses.parseNumericAddress(DNS_IP_ADDR_1));
-        dnsServers.add(InetAddresses.parseNumericAddress(DNS_IP_ADDR_2));
-        final StaticIpConfiguration staticIpConfiguration1 = new StaticIpConfiguration.Builder()
-                .setIpAddress(new LinkAddress(IP_ADDR_1))
-                .setDnsServers(dnsServers).build();
-        final StaticIpConfiguration staticIpConfiguration2 = new StaticIpConfiguration.Builder()
-                .setIpAddress(new LinkAddress(IP_ADDR_2))
-                .setDnsServers(dnsServers).build();
+        final IpConfiguration expectedConfig1 = newIpConfiguration(IpAssignment.STATIC,
+                ProxySettings.STATIC, STATIC_IP_CONFIG_1, PROXY_INFO);
+        final IpConfiguration expectedConfig2 = newIpConfiguration(IpAssignment.STATIC,
+                ProxySettings.STATIC, STATIC_IP_CONFIG_2, PROXY_INFO);
 
-        ProxyInfo proxyInfo =
-                ProxyInfo.buildDirectProxy("10.10.10.10", 88, Arrays.asList("host1", "host2"));
-
-        IpConfiguration expectedConfig1 = newIpConfiguration(IpAssignment.STATIC,
-                ProxySettings.STATIC, staticIpConfiguration1, proxyInfo);
-        IpConfiguration expectedConfig2 = newIpConfiguration(IpAssignment.STATIC,
-                ProxySettings.STATIC, staticIpConfiguration2, proxyInfo);
-
-        ArrayMap<String, IpConfiguration> expectedNetworks = new ArrayMap<>();
+        final ArrayMap<String, IpConfiguration> expectedNetworks = new ArrayMap<>();
         expectedNetworks.put(IFACE_1, expectedConfig1);
         expectedNetworks.put(IFACE_2, expectedConfig2);
 
-        MockedDelayedDiskWrite writer = new MockedDelayedDiskWrite();
-        IpConfigStore store = new IpConfigStore(writer);
+        final MockedDelayedDiskWrite writer = new MockedDelayedDiskWrite();
+        final IpConfigStore store = new IpConfigStore(writer);
         store.writeIpConfigurations("file/path/not/used/", expectedNetworks);
 
-        InputStream in = new ByteArrayInputStream(writer.mByteStream.toByteArray());
-        ArrayMap<String, IpConfiguration> actualNetworks = IpConfigStore.readIpConfigurations(in);
+        final InputStream in = new ByteArrayInputStream(writer.mByteStream.toByteArray());
+        final ArrayMap<String, IpConfiguration> actualNetworks =
+                IpConfigStore.readIpConfigurations(in);
         assertNotNull(actualNetworks);
         assertEquals(2, actualNetworks.size());
         assertEquals(expectedNetworks.get(IFACE_1), actualNetworks.get(IFACE_1));
         assertEquals(expectedNetworks.get(IFACE_2), actualNetworks.get(IFACE_2));
     }
 
+    @Test
+    public void readIpConfigurationFromFilePath() throws Exception {
+        final HandlerThread testHandlerThread = new HandlerThread("IpConfigStoreTest");
+        final DelayedDiskWrite.Dependencies dependencies =
+                new DelayedDiskWrite.Dependencies() {
+                    @Override
+                    public HandlerThread makeHandlerThread() {
+                        return testHandlerThread;
+                    }
+                    @Override
+                    public void quitHandlerThread(HandlerThread handlerThread) {
+                        testHandlerThread.quitSafely();
+                    }
+        };
+
+        final IpConfiguration ipConfig = newIpConfiguration(IpAssignment.STATIC,
+                ProxySettings.STATIC, STATIC_IP_CONFIG_1, PROXY_INFO);
+        final ArrayMap<String, IpConfiguration> expectedNetworks = new ArrayMap<>();
+        expectedNetworks.put(IFACE_1, ipConfig);
+
+        // Write IP config to specific file path and read it later.
+        final Context context = InstrumentationRegistry.getContext();
+        final File configFile = new File(context.getFilesDir().getPath(),
+                "IpConfigStoreTest-ipconfig.txt");
+        final DelayedDiskWrite writer = new DelayedDiskWrite(dependencies);
+        final IpConfigStore store = new IpConfigStore(writer);
+        store.writeIpConfigurations(configFile.getPath(), expectedNetworks);
+        HandlerUtils.waitForIdle(testHandlerThread, TIMEOUT_MS);
+
+        // Read IP config from the file path.
+        final ArrayMap<String, IpConfiguration> actualNetworks =
+                IpConfigStore.readIpConfigurations(configFile.getPath());
+        assertNotNull(actualNetworks);
+        assertEquals(1, actualNetworks.size());
+        assertEquals(expectedNetworks.get(IFACE_1), actualNetworks.get(IFACE_1));
+
+        // Return an empty array when reading IP configuration from an non-exist config file.
+        final ArrayMap<String, IpConfiguration> emptyNetworks =
+                IpConfigStore.readIpConfigurations("/dev/null");
+        assertNotNull(emptyNetworks);
+        assertEquals(0, emptyNetworks.size());
+
+        configFile.delete();
+    }
+
     private IpConfiguration newIpConfiguration(IpAssignment ipAssignment,
             ProxySettings proxySettings, StaticIpConfiguration staticIpConfig, ProxyInfo info) {
         final IpConfiguration config = new IpConfiguration();