FileAndWeakByteSource fileAndSource = leakFileBackedOutputStream();
    File file = fileAndSource.file;
    WeakReference<ByteSource> sourceRef = fileAndSource.sourceRef;
    fileAndSource = null;
    awaitClear(sourceRef);
    awaitDone(() -> !file.exists());
  }

  private static final class FileAndWeakByteSource {
    final File file;