diff --git a/testutils/src/main/java/com/google/android/exoplayer2/testutil/DataSourceContractTest.java b/testutils/src/main/java/com/google/android/exoplayer2/testutil/DataSourceContractTest.java
index 4bce4a11aba..c785145a537 100644
--- a/testutils/src/main/java/com/google/android/exoplayer2/testutil/DataSourceContractTest.java
+++ b/testutils/src/main/java/com/google/android/exoplayer2/testutil/DataSourceContractTest.java
@@ -24,7 +24,6 @@
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 
@@ -391,8 +390,10 @@ public void transferListenerCallbacks() throws Exception {
     for (int i = 0; i < resources.size(); i++) {
       additionalFailureInfo.setInfo(getFailureLabel(resources, i));
       DataSource dataSource = createDataSource();
-      FakeTransferListener listener = spy(new FakeTransferListener());
-      dataSource.addTransferListener(listener);
+      TransferListener listener = mock(TransferListener.class);
+      ByteCountingTransferListener byteCountingTransferListener =
+          new ByteCountingTransferListener(listener);
+      dataSource.addTransferListener(byteCountingTransferListener);
       InOrder inOrder = Mockito.inOrder(listener);
       @Nullable DataSource callbackSource = getTransferListenerDataSource();
       if (callbackSource == null) {
@@ -430,7 +431,8 @@ public void transferListenerCallbacks() throws Exception {
         }
         // Verify sufficient onBytesTransferred() callbacks have been triggered before closing the
         // DataSource.
-        assertThat(listener.bytesTransferred).isAtLeast(resource.getExpectedBytes().length);
+        assertThat(byteCountingTransferListener.bytesTransferred)
+            .isAtLeast(resource.getExpectedBytes().length);
 
       } finally {
         dataSource.close();
@@ -615,23 +617,37 @@ public TestResource build() {
     }
   }
 
-  /** A {@link TransferListener} that only keeps track of the transferred bytes. */
-  public static class FakeTransferListener implements TransferListener {
+  /** A {@link TransferListener} that keeps track of the transferred bytes. */
+  private static final class ByteCountingTransferListener implements TransferListener {
+
+    private final TransferListener transferListener;
+
     private int bytesTransferred;
 
+    public ByteCountingTransferListener(TransferListener transferListener) {
+      this.transferListener = transferListener;
+    }
+
     @Override
-    public void onTransferInitializing(DataSource source, DataSpec dataSpec, boolean isNetwork) {}
+    public void onTransferInitializing(DataSource source, DataSpec dataSpec, boolean isNetwork) {
+      transferListener.onTransferInitializing(source, dataSpec, isNetwork);
+    }
 
     @Override
-    public void onTransferStart(DataSource source, DataSpec dataSpec, boolean isNetwork) {}
+    public void onTransferStart(DataSource source, DataSpec dataSpec, boolean isNetwork) {
+      transferListener.onTransferStart(source, dataSpec, isNetwork);
+    }
 
     @Override
     public void onBytesTransferred(
         DataSource source, DataSpec dataSpec, boolean isNetwork, int bytesTransferred) {
+      transferListener.onBytesTransferred(source, dataSpec, isNetwork, bytesTransferred);
       this.bytesTransferred += bytesTransferred;
     }
 
     @Override
-    public void onTransferEnd(DataSource source, DataSpec dataSpec, boolean isNetwork) {}
+    public void onTransferEnd(DataSource source, DataSpec dataSpec, boolean isNetwork) {
+      transferListener.onTransferEnd(source, dataSpec, isNetwork);
+    }
   }
 }