我正在开发一个下载管理器使用UP设计。在这个精化迭代中，我的主要用例是:下载文件。这是Download.java
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) {}
}
}
}
如何编写这段代码的测试代码?例如，我应该测试URL验证，还是应该控制文件是否正在下载?我怎么做这些检查?谢谢。
您编写的类很难测试，因为它试图做的事情太多了。如果您要将一些职责提取到外部依赖项中，那么您最终可能会得到一个类来管理来自url的低级下载，而另一个类来管理本地文件系统。比如:
interface UrlDownloader {
InputStream download(URL url, int offset) throws IOException;
}
interface DownloadFolder {
List<String> getFiles();
void writeToFile(String filename, InputStream contents) throws IOException;
void getFileSize(String filename);
}
@Test
public void canDownloadCompleteFile() throws IOException {
URL url = new URL("http://example.com/file.txt");
InputStream inputStream = new ByteArrayInputStream("abc".getBytes());
UrlDownloader urlDownloader = mock(UrlDownloader.class);
DownloadFolder downloadFolder = mock(DownloadFolder.class);
when(urlDownloader.download(url, 0)).thenReturn(inputStream);
DownloadManager manager = new DownloadManager(urlDownloader, downloadFolder);
manager.download(url);
verify(downloadFolder).writeToFile("file.txt", inputStream);
}
使用mockito，您可以控制依赖项何时抛出异常，或者验证使用特定参数调用方法。
另一种方法是创建伪类来实现您的接口，并使用内存中的数据结构而不是真正的文件系统/网络。然后可以使用assertEquals等来测试这些类的状态:
@Test
public void canDownloadCompleteFile() throws IOException {
URL url = new URL("http://example.com/file.txt");
FakeDownloadFolder downloadFolder = new FakeDownloadFolder();
FakeUrlDownloader urlDownloader = new FakeUrlDownloader();
urlDownloader.setUrlContents(url, "abc".getBytes());
DownloadManager manager = new DownloadManager(urlDownloader, downloadFolder);
manager.download(url);
assertEquals("abc".getBytes(), downloadFolder.getFileAsByteArray("file.txt"));
}
测试驱动开发背后的思想是，您只编写由测试支持的代码。所以你需要实现足够的DownloadManager来通过第一个测试，然后添加另一个测试(例如，恢复未完成的下载)。
回答你的直接问题:为这些代码写一个测试真的很难。
单元测试的美妙之处在于，它们向您展示了代码的客户端使用模块是多么容易。有一个很大的领域叫做"面向对象的分析与设计"，旨在帮助程序员解决这些问题。
在这里，你应该改变你的代码，有几个例程具有单一的责任，例如，一个用于网络通信，一个用于存储自定义数据流到硬盘，另一个用于处理使用输入。这样你就可以单独测试这些"例程"，甚至提供你自己的"网络"环境(例如，类将放置硬编码值而不是真正连接到网络)