java - ダウンロード マネージャー用のテスト駆動型 Java クラスを作成するにはどうすればよいですか?

Question

UP Design を使用してダウンロード マネージャーを開発しています。

public class Download  implements Runnable {

// Max size of download buffer.
private static final int MAX_BUFFER_SIZE = 1024;

// These are the status names.
public static final String STATUSES[] = {"Downloading", "Complete"};

// These are the status codes.
public static final int DOWNLOADING = 0;
public static final int COMPLETE = 1;
public static void main(String[] args) throws MalformedURLException {
    System.out.println("Welcome to Download Manager.");
    System.out.println("Enter a URL.");
    URL url;
    String s;
    Scanner scan= new Scanner(System.in);
    s=scan.nextLine();
    url= new URL(s);
    Download download=new Download(url);

}

private URL url; // download URL
private int size; // size of download in bytes
private int downloaded; // number of bytes downloaded
private int status; // current status of download

// Constructor for Download.
public Download(URL url) {
    this.url = url;
    size = -1;
    downloaded = 0;
    status = DOWNLOADING;

    // Begin the download.
    download();
}
 // Start or resume downloading.
private void download() {
    System.out.println("Starting.");
    Thread thread = new Thread(this);
    thread.start();
}
// Download file.
public void run() {
    RandomAccessFile file = null;
    InputStream stream = null;

    try {
        // Open connection to URL.
        HttpURLConnection connection =
                (HttpURLConnection) url.openConnection();

        // Specify what portion of file to download.
        connection.setRequestProperty("Range",
                "bytes=" + downloaded + "-");

        // Connect to server.
        connection.connect();


        int contentLength = connection.getContentLength();


  /* Set the size for this download if it
     hasn't been already set. */
        if (size == -1) {
            size = contentLength;

        }

        // Open file and seek to the end of it.
        file = new RandomAccessFile(getFileName(url), "rw");
        file.seek(downloaded);

        stream = connection.getInputStream();
        while (status == DOWNLOADING) {
    /* Size buffer according to how much of the
       file is left to download. */
            byte buffer[];
            if (size - downloaded > MAX_BUFFER_SIZE) {
                buffer = new byte[MAX_BUFFER_SIZE];
            } else {
                buffer = new byte[size - downloaded];
            }
            System.out.print("%"+(downloaded/size)+'\r');
            // Read from server into buffer.
            int read = stream.read(buffer);
            if (read == -1){
                System.out.println("File was downloaded");
                break;
            }

            // Write buffer to file.
            file.write(buffer, 0, read);
            downloaded += read;

        }

  /* Change status to complete if this point was
     reached because downloading has finished. */
        if (status == DOWNLOADING) {
            status = COMPLETE;

        }
    } catch (Exception e) {
       System.out.println("Error!");
    } finally {
        // Close file.
        if (file != null) {
            try {
                file.close();
            } catch (Exception e) {}
        }

        // Close connection to server.
        if (stream != null) {
            try {
                stream.close();
            } catch (Exception e) {}
        }
    }
}

このコードのテスト コードをどのように記述すればよいですか?たとえば、URL の検証をテストする必要がありますか?または、ファイルがダウンロードされているかどうかを制御する必要がありますか?これらのテストを行うにはどうすればよいですか? ありがとう。