diff --git a/tests/unit/src/com/android/networkstack/metrics/DataStallStatsUtilsTest.kt b/tests/unit/src/com/android/networkstack/metrics/DataStallStatsUtilsTest.kt
index 4c62071..578e6ca 100644
--- a/tests/unit/src/com/android/networkstack/metrics/DataStallStatsUtilsTest.kt
+++ b/tests/unit/src/com/android/networkstack/metrics/DataStallStatsUtilsTest.kt
@@ -16,18 +16,33 @@
 
 package com.android.networkstack.metrics
 
+import android.net.NetworkCapabilities.TRANSPORT_CELLULAR
 import android.net.captiveportal.CaptivePortalProbeResult
+import android.net.metrics.ValidationProbeEvent
+import android.net.util.DataStallUtils.DATA_STALL_EVALUATION_TYPE_DNS
+import android.telephony.TelephonyManager
 import androidx.test.filters.SmallTest
 import androidx.test.runner.AndroidJUnit4
+import com.android.dx.mockito.inline.extended.ExtendedMockito.mockitoSession
+import com.android.dx.mockito.inline.extended.ExtendedMockito.verify
+import com.android.server.connectivity.nano.CellularData
 import com.android.server.connectivity.nano.DataStallEventProto
+import com.android.server.connectivity.nano.DnsEvent
+import com.google.protobuf.nano.MessageNano
+import java.util.Arrays
 import org.junit.Assert.assertEquals
 import org.junit.Test
 import org.junit.runner.RunWith
-import android.net.metrics.ValidationProbeEvent
+import org.mockito.ArgumentMatchers.eq
 
 @RunWith(AndroidJUnit4::class)
 @SmallTest
 class DataStallStatsUtilsTest {
+    private val TEST_ELAPSED_TIME_MS = 123456789L
+    private val TEST_MCCMNC = "123456"
+    private val TEST_SIGNAL_STRENGTH = -100
+    private val RETURN_CODE_DNS_TIMEOUT = 255
+
     @Test
     fun testProbeResultToEnum() {
         assertEquals(DataStallStatsUtils.probeResultToEnum(null), DataStallEventProto.INVALID)
@@ -53,4 +68,61 @@
                 CaptivePortalProbeResult.PORTAL_CODE, ValidationProbeEvent.PROBE_HTTPS)),
                 DataStallEventProto.PORTAL)
     }
+
+    @Test
+    fun testWrite() {
+        val session = mockitoSession().spyStatic(NetworkStackStatsLog::class.java).startMocking()
+        val stats = DataStallDetectionStats.Builder()
+                .setEvaluationType(DATA_STALL_EVALUATION_TYPE_DNS)
+                .setNetworkType(TRANSPORT_CELLULAR)
+                .setCellData(TelephonyManager.NETWORK_TYPE_LTE /* radioType */,
+                        true /* roaming */,
+                        TEST_MCCMNC /* networkMccmnc */,
+                        TEST_MCCMNC /* simMccmnc */,
+                        TEST_SIGNAL_STRENGTH /* signalStrength */)
+                .setTcpFailRate(90)
+                .setTcpSentSinceLastRecv(10)
+        generateTimeoutDnsEvent(stats, count = 5)
+        DataStallStatsUtils.write(stats.build(), CaptivePortalProbeResult.PARTIAL)
+
+        verify { NetworkStackStatsLog.write(
+                eq(NetworkStackStatsLog.DATA_STALL_EVENT),
+                eq(DATA_STALL_EVALUATION_TYPE_DNS),
+                eq(DataStallEventProto.PARTIAL),
+                eq(TRANSPORT_CELLULAR),
+                eq(DataStallDetectionStats.emptyWifiInfoIfNull(null)),
+                eq(makeTestCellDataNano()),
+                eq(makeTestDnsTimeoutNano(5)),
+                eq(90) /* tcpFailRate */,
+                eq(10) /* tcpSentSinceLastRecv */) }
+
+        session.finishMocking()
+    }
+
+    private fun makeTestDnsTimeoutNano(timeoutCount: Int): ByteArray? {
+        // Make an expected nano dns message.
+        val event = DnsEvent()
+        event.dnsReturnCode = IntArray(timeoutCount)
+        event.dnsTime = LongArray(timeoutCount)
+        Arrays.fill(event.dnsReturnCode, RETURN_CODE_DNS_TIMEOUT)
+        Arrays.fill(event.dnsTime, TEST_ELAPSED_TIME_MS)
+        return MessageNano.toByteArray(event)
+    }
+
+    private fun makeTestCellDataNano(): ByteArray? {
+        // Make an expected nano cell data message.
+        val data = CellularData()
+        data.ratType = DataStallEventProto.RADIO_TECHNOLOGY_LTE
+        data.networkMccmnc = TEST_MCCMNC
+        data.simMccmnc = TEST_MCCMNC
+        data.isRoaming = true
+        data.signalStrength = TEST_SIGNAL_STRENGTH
+        return MessageNano.toByteArray(data)
+    }
+
+    private fun generateTimeoutDnsEvent(stats: DataStallDetectionStats.Builder, count: Int) {
+        repeat(count) {
+            stats.addDnsEvent(RETURN_CODE_DNS_TIMEOUT, TEST_ELAPSED_TIME_MS)
+        }
+    }
 }