diff --git a/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/ClippingMediaSourceTest.java b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/ClippingMediaSourceTest.java
index 9b30ffd14f..cbf435018f 100644
--- a/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/ClippingMediaSourceTest.java
+++ b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/ClippingMediaSourceTest.java
@@ -610,8 +610,7 @@ public final class ClippingMediaSourceTest {
       ClippingMediaSource clippingMediaSource,
       Timeline... additionalTimelines)
       throws IOException {
-    MediaSourceTestRunner testRunner =
-        new MediaSourceTestRunner(clippingMediaSource, /* allocator= */ null);
+    MediaSourceTestRunner testRunner = new MediaSourceTestRunner(clippingMediaSource);
     Timeline[] clippedTimelines = new Timeline[additionalTimelines.length + 1];
     try {
       clippedTimelines[0] = testRunner.prepareSource();
diff --git a/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/ConcatenatingMediaSourceTest.java b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/ConcatenatingMediaSourceTest.java
index 860abc5282..6533dbd257 100644
--- a/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/ConcatenatingMediaSourceTest.java
+++ b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/ConcatenatingMediaSourceTest.java
@@ -55,7 +55,7 @@ public final class ConcatenatingMediaSourceTest {
   @Before
   public void setUp() throws Exception {
     mediaSource = new ConcatenatingMediaSource(/* isAtomic= */ false, new FakeShuffleOrder(0));
-    testRunner = new MediaSourceTestRunner(mediaSource, null);
+    testRunner = new MediaSourceTestRunner(mediaSource);
   }
 
   @After
@@ -722,7 +722,7 @@ public final class ConcatenatingMediaSourceTest {
     testRunner.release();
     ConcatenatingMediaSource mediaSource =
         new ConcatenatingMediaSource(/* isAtomic= */ true, new FakeShuffleOrder(0));
-    testRunner = new MediaSourceTestRunner(mediaSource, null);
+    testRunner = new MediaSourceTestRunner(mediaSource);
     mediaSource.addMediaSources(Arrays.asList(createMediaSources(3)));
     Timeline timeline = testRunner.prepareSource();
     TimelineAsserts.assertWindowTags(timeline, 111, 222, 333);
@@ -958,7 +958,7 @@ public final class ConcatenatingMediaSourceTest {
             /* useLazyPreparation= */ true,
             new DefaultShuffleOrder(0),
             childSources);
-    testRunner = new MediaSourceTestRunner(mediaSource, /* allocator= */ null);
+    testRunner = new MediaSourceTestRunner(mediaSource);
     testRunner.prepareSource();
 
     assertThat(childSources[0].isPrepared()).isFalse();
@@ -974,7 +974,7 @@ public final class ConcatenatingMediaSourceTest {
             /* useLazyPreparation= */ true,
             new DefaultShuffleOrder(0),
             childSources);
-    testRunner = new MediaSourceTestRunner(mediaSource, /* allocator= */ null);
+    testRunner = new MediaSourceTestRunner(mediaSource);
     Timeline timeline = testRunner.prepareSource();
     testRunner.createPeriod(
         new MediaPeriodId(
@@ -993,7 +993,7 @@ public final class ConcatenatingMediaSourceTest {
             /* useLazyPreparation= */ true,
             new DefaultShuffleOrder(0),
             childSources);
-    testRunner = new MediaSourceTestRunner(mediaSource, /* allocator= */ null);
+    testRunner = new MediaSourceTestRunner(mediaSource);
     Timeline timeline = testRunner.prepareSource();
 
     // The lazy preparation must only be triggered once, even if we create multiple periods from
@@ -1015,7 +1015,7 @@ public final class ConcatenatingMediaSourceTest {
             /* useLazyPreparation= */ true,
             new DefaultShuffleOrder(0),
             childSources);
-    testRunner = new MediaSourceTestRunner(mediaSource, /* allocator= */ null);
+    testRunner = new MediaSourceTestRunner(mediaSource);
     testRunner.prepareSource();
 
     // Check that removal doesn't throw even though the child sources are unprepared.
diff --git a/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/LoopingMediaSourceTest.java b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/LoopingMediaSourceTest.java
index 6e8f84a8c3..fb15aaf4d2 100644
--- a/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/LoopingMediaSourceTest.java
+++ b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/LoopingMediaSourceTest.java
@@ -167,7 +167,7 @@ public class LoopingMediaSourceTest {
   private static Timeline getLoopingTimeline(Timeline timeline, int loopCount) throws IOException {
     FakeMediaSource fakeMediaSource = new FakeMediaSource(timeline);
     LoopingMediaSource mediaSource = new LoopingMediaSource(fakeMediaSource, loopCount);
-    MediaSourceTestRunner testRunner = new MediaSourceTestRunner(mediaSource, null);
+    MediaSourceTestRunner testRunner = new MediaSourceTestRunner(mediaSource);
     try {
       Timeline loopingTimeline = testRunner.prepareSource();
       testRunner.releaseSource();
@@ -185,7 +185,7 @@ public class LoopingMediaSourceTest {
   private static void testMediaPeriodCreation(Timeline timeline, int loopCount) throws Exception {
     FakeMediaSource fakeMediaSource = new FakeMediaSource(timeline);
     LoopingMediaSource mediaSource = new LoopingMediaSource(fakeMediaSource, loopCount);
-    MediaSourceTestRunner testRunner = new MediaSourceTestRunner(mediaSource, null);
+    MediaSourceTestRunner testRunner = new MediaSourceTestRunner(mediaSource);
     try {
       testRunner.prepareSource();
       testRunner.assertPrepareAndReleaseAllPeriods();
diff --git a/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/MergingMediaSourceTest.java b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/MergingMediaSourceTest.java
index 373286f459..f45adbd4a5 100644
--- a/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/MergingMediaSourceTest.java
+++ b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/MergingMediaSourceTest.java
@@ -99,7 +99,7 @@ public class MergingMediaSourceTest {
       mediaSources[i] = new FakeMediaSource(new FakeTimeline(/* windowCount= */ 2));
     }
     MergingMediaSource mediaSource = new MergingMediaSource(mediaSources);
-    MediaSourceTestRunner testRunner = new MediaSourceTestRunner(mediaSource, null);
+    MediaSourceTestRunner testRunner = new MediaSourceTestRunner(mediaSource);
     try {
       testRunner.prepareSource();
       testRunner.assertPrepareAndReleaseAllPeriods();
@@ -124,8 +124,7 @@ public class MergingMediaSourceTest {
     }
     MergingMediaSource mergingMediaSource =
         new MergingMediaSource(/* adjustPeriodTimeOffsets= */ false, clipDurations, mediaSources);
-    MediaSourceTestRunner testRunner =
-        new MediaSourceTestRunner(mergingMediaSource, /* allocator= */ null);
+    MediaSourceTestRunner testRunner = new MediaSourceTestRunner(mergingMediaSource);
     try {
       Timeline timeline = testRunner.prepareSource();
       testRunner.releaseSource();
diff --git a/libraries/test_utils/src/main/java/androidx/media3/test/utils/MediaSourceTestRunner.java b/libraries/test_utils/src/main/java/androidx/media3/test/utils/MediaSourceTestRunner.java
index 34e7966b8b..186ce8e430 100644
--- a/libraries/test_utils/src/main/java/androidx/media3/test/utils/MediaSourceTestRunner.java
+++ b/libraries/test_utils/src/main/java/androidx/media3/test/utils/MediaSourceTestRunner.java
@@ -26,6 +26,7 @@ import android.os.HandlerThread;
 import android.os.Looper;
 import android.util.Pair;
 import androidx.annotation.Nullable;
+import androidx.media3.common.C;
 import androidx.media3.common.Timeline;
 import androidx.media3.common.util.Assertions;
 import androidx.media3.common.util.NullableType;
@@ -40,6 +41,7 @@ import androidx.media3.exoplayer.source.MediaSource.MediaPeriodId;
 import androidx.media3.exoplayer.source.MediaSource.MediaSourceCaller;
 import androidx.media3.exoplayer.source.MediaSourceEventListener;
 import androidx.media3.exoplayer.upstream.Allocator;
+import androidx.media3.exoplayer.upstream.DefaultAllocator;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -68,12 +70,13 @@ public class MediaSourceTestRunner {
   @Nullable private Timeline timeline;
 
   /**
+   * Creates an instance.
+   *
    * @param mediaSource The source under test.
-   * @param allocator The allocator to use during the test run.
    */
-  public MediaSourceTestRunner(MediaSource mediaSource, Allocator allocator) {
+  public MediaSourceTestRunner(MediaSource mediaSource) {
     this.mediaSource = mediaSource;
-    this.allocator = allocator;
+    this.allocator = new DefaultAllocator(true, C.DEFAULT_BUFFER_SEGMENT_SIZE);
     playbackThread = new HandlerThread("TestHandler");
     playbackThread.start();
     Looper playbackLooper = playbackThread.getLooper();