System.out.println（）的JUnit测试 [英] JUnit test for System.out.println()

问题描述

我需要为一个设计不良的旧应用程序编写JUnit测试，并且正在向标准输出写入大量错误消息。当 getResponse（String request）方法正确运行时，它返回一个XML响应：

I need to write JUnit tests for an old application that's poorly designed and is writing a lot of error messages to standard output. When the getResponse(String request) method behaves correctly it returns a XML response:

@BeforeClass
public static void setUpClass() throws Exception {
    Properties queries = loadPropertiesFile("requests.properties");
    Properties responses = loadPropertiesFile("responses.properties");
    instance = new ResponseGenerator(queries, responses);
}

@Test
public void testGetResponse() {
    String request = "<some>request</some>";
    String expResult = "<some>response</some>";
    String result = instance.getResponse(request);
    assertEquals(expResult, result);
}

但是当它得到格式不正确的XML或不理解请求时，返回<$

But when it gets malformed XML or does not understand the request it returns null and writes some stuff to standard output.

有没有办法在JUnit中声明控制台输出？c $ c> null 捕获如下情况：

Is there any way to assert console output in JUnit? To catch cases like:

System.out.println("match found: " + strExpr);
System.out.println("xml not well formed: " + e.getMessage());

推荐答案

使用 ByteArrayOutputStream 和System.setXXX很简单：

using ByteArrayOutputStream and System.setXXX is simple:

private final ByteArrayOutputStream outContent = new ByteArrayOutputStream();
private final ByteArrayOutputStream errContent = new ByteArrayOutputStream();

@Before
public void setUpStreams() {
    System.setOut(new PrintStream(outContent));
    System.setErr(new PrintStream(errContent));
}

@After
public void cleanUpStreams() {
    System.setOut(null);
    System.setErr(null);
}

样本测试用例：

@Test
public void out() {
    System.out.print("hello");
    assertEquals("hello", outContent.toString());
}

@Test
public void err() {
    System.err.print("hello again");
    assertEquals("hello again", errContent.toString());
}

我使用这个代码来测试命令行选项版本字符串等）

I used this code to test the command line option (asserting that -version outputs the version string, etc etc)

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