如何从android Junit ServiceTestCase复制setUp方法中的资产文件？

@Override
protected void setUp() throws Exception {
    super.setUp();
    Context context = getContext();
    AssetManager assetManager = context.getAssets();
    InputStream inputStream = assetManager.open("your_asset_file.txt");
    File targetFile = new File(context.getFilesDir(), "your_asset_file.txt");
    FileOutputStream outputStream = new FileOutputStream(targetFile);
    byte[] buffer = new byte[1024];
    int length;
    while ((length = inputStream.read(buffer)) != -1) {
        outputStream.write(buffer, 0, length);
    }
    inputStream.close();
    outputStream.close();
}