diff --git a/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/source/BaseMediaSource.java b/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/source/BaseMediaSource.java
index a2b0d46096..d4b456391e 100644
--- a/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/source/BaseMediaSource.java
+++ b/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/source/BaseMediaSource.java
@@ -179,12 +179,29 @@ public abstract class BaseMediaSource implements MediaSource {
    * Returns the {@link PlayerId} of the player using this media source.
    *
    * <p>Must only be used when the media source is {@link #prepareSourceInternal(TransferListener)
-   * prepared}.
+   * prepared} or has {@linkplain #setPlayerId a player ID set}.
    */
   protected final PlayerId getPlayerId() {
     return checkStateNotNull(playerId);
   }
 
+  /**
+   * Sets the {@link PlayerId} of the player using this media source.
+   *
+   * @param playerId The player ID to be set.
+   */
+  protected final void setPlayerId(PlayerId playerId) {
+    this.playerId = playerId;
+  }
+
+  /**
+   * Returns whether the source has {@link MediaSource#prepareSource(MediaSourceCaller,
+   * TransferListener, PlayerId)} called.
+   */
+  protected final boolean prepareSourceCalled() {
+    return !mediaSourceCallers.isEmpty();
+  }
+
   @Override
   public final void addEventListener(Handler handler, MediaSourceEventListener eventListener) {
     Assertions.checkNotNull(handler);
diff --git a/libraries/test_utils/src/main/java/androidx/media3/test/utils/FakeMediaSourceFactory.java b/libraries/test_utils/src/main/java/androidx/media3/test/utils/FakeMediaSourceFactory.java
index 307ec5bbe9..62cbfddcaa 100644
--- a/libraries/test_utils/src/main/java/androidx/media3/test/utils/FakeMediaSourceFactory.java
+++ b/libraries/test_utils/src/main/java/androidx/media3/test/utils/FakeMediaSourceFactory.java
@@ -15,6 +15,8 @@
  */
 package androidx.media3.test.utils;
 
+import static androidx.media3.common.util.Assertions.checkNotNull;
+
 import androidx.media3.common.AdPlaybackState;
 import androidx.media3.common.C;
 import androidx.media3.common.MediaItem;
@@ -26,6 +28,7 @@ import androidx.media3.exoplayer.source.MediaSourceFactory;
 import androidx.media3.exoplayer.upstream.LoadErrorHandlingPolicy;
 import androidx.media3.test.utils.FakeTimeline.TimelineWindowDefinition;
 import com.google.common.collect.ImmutableList;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
 /** Fake {@link MediaSourceFactory} that creates a {@link FakeMediaSource}. */
 @UnstableApi
@@ -36,6 +39,18 @@ public final class FakeMediaSourceFactory implements MediaSourceFactory {
   /** The window UID used by media sources that are created by the factory. */
   public static final Object DEFAULT_WINDOW_UID = new Object();
 
+  private @MonotonicNonNull FakeMediaSource lastCreatedSource;
+
+  /**
+   * Returns the last created {@link FakeMediaSource}.
+   *
+   * <p>Must be called after at least one {@link FakeMediaSource} is {@link
+   * FakeMediaSourceFactory#createMediaSource(MediaItem) created}.
+   */
+  public FakeMediaSource getLastCreatedSource() {
+    return checkNotNull(lastCreatedSource);
+  }
+
   @Override
   public MediaSourceFactory setDrmSessionManagerProvider(
       DrmSessionManagerProvider drmSessionManagerProvider) {
@@ -68,6 +83,7 @@ public final class FakeMediaSourceFactory implements MediaSourceFactory {
             /* windowOffsetInFirstPeriodUs= */ Util.msToUs(123456789),
             ImmutableList.of(AdPlaybackState.NONE),
             mediaItem);
-    return new FakeMediaSource(new FakeTimeline(timelineWindowDefinition));
+    lastCreatedSource = new FakeMediaSource(new FakeTimeline(timelineWindowDefinition));
+    return lastCreatedSource;
   }
 }