JUnit完全无效的方法

Question

如何测试像这样的复杂void方法：

public void saveFileToDisk(BtrUploadedDoc uploadedDoc , NewEvenDTO newEvent) {

        try {

        File targetFolder = new File(uploadedDoc.getFilePath()); 
        InputStream inputStream = newEvent.getUploadedFile().getInputstream();
        OutputStream out = new FileOutputStream(new File(targetFolder, uploadedDoc.getUpdoId().toString() + uploadedDoc.getFileExt()));

        int read = 0;

        byte[] bytes = new byte[1024];
        while ((read = inputStream.read(bytes)) != -1) {

            out.write(bytes, 0, read);

        }
        inputStream.close();
        out.flush();
        out.close();
        }
        catch (Exception ex) {
            log.error("Disk write error: " + ex.getMessage(), ex);

        }

    }

抱歉，但我不知道如何开始。我的文章很多，但所有教程都是关于简单返回值的简单方法。谢谢！