Java、Junit - 捕获用于单元测试的标准输入/输出
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Java, Junit - Capture the standard input / Output for use in a unit test
提问by Frank V
I'm writing integration tests using JUnit to automate the testing of a console based application. The application is homework but this part isn't the homework. I want to automate these tests to be more productive -- I don't want to have to go back and retest already tested parts of the application. (Standard reasons to use Unit tests)
我正在使用 JUnit 编写集成测试来自动化基于控制台的应用程序的测试。申请是作业，但这部分不是作业。我想自动化这些测试以提高效率——我不想回去重新测试应用程序中已经测试过的部分。（使用单元测试的标准理由）
Anyway, I can't figure out or find an article on capturing the output so that I can do assertEqualson it nor providing automated input. I don't care if the output/input goes to the console/output pane. I only need to have the test execute and verify the the output is what is expected given the input.
无论如何，我无法弄清楚或找到有关捕获输出的文章，以便我可以对其进行assertEquals处理，也无法提供自动输入。我不在乎输出/输入是否进入控制台/输出窗格。我只需要执行测试并验证输出是给定输入的预期结果。
Anyone have an article or code to help out with this.
任何人都有一篇文章或代码来帮助解决这个问题。
采纳答案by Andrzej Doyle
Use System.setOut()(and System.setErr()) to redirect the output to an arbitrary printstream - which can be one that you read from programmatically.
使用System.setOut()（和System.setErr()）将输出重定向到任意打印流 - 可以是您以编程方式读取的打印流。
For example:
例如：
final ByteArrayOutputStream myOut = new ByteArrayOutputStream();
System.setOut(new PrintStream(myOut));
// test stuff here...
final String standardOutput = myOut.toString();
回答by Michael Borgwardt
The Systemclass has methods setIn(), setOut()and setErr()that allow you to set the standard input, output and error streams, e.g. to a ByteArrayOutputStreamthat you can inspect at will.
本System类有方法setIn()，setOut()并setErr()允许您的标准输入，输出和错误流，如设为ByteArrayOutputStream您可以将检查。
回答by Val
Here is the solution in place of ByteArrayOutputStream. It does not add anything to the idea of System.setOut. Rather, I want to share the implementation that is better than capturing everything into ByteArrayOutputStream. I prefer to capture only selected information and let all log messages to appear in the console as they are logged rather than capturing everything into a balckbox (of which size?) for later processing.
这是替代 ByteArrayOutputStream 的解决方案。它不会为 System.setOut 的想法添加任何内容。相反，我想分享比将所有内容捕获到 ByteArrayOutputStream 中更好的实现。我更喜欢只捕获选定的信息，并让所有日志消息在记录时显示在控制台中，而不是将所有内容捕获到一个黑匣子（大小？）中以供以后处理。
/**
* Once started, std output is redirected to this thread.
* Thread redirects all data to the former system.out and
* captures some strings.*/
static abstract class OutputCaputre extends Thread {
// overrdie these methods for System.err
PrintStream getDownstream() { return System.out;}
void restoreDownstream() { System.setOut(downstream);}
// will be called for every line in the log
protected abstract void userFilter(String line);
final PrintStream downstream;
public final PipedInputStream pis;
private final PipedOutputStream pos;
OutputCaputre() throws IOException {
downstream = getDownstream();
pos = new PipedOutputStream();
pis = new PipedInputStream(pos);
System.setOut(new PrintStream(pos));
start();
}
public void run() {
try {
BufferedReader br = new BufferedReader(new InputStreamReader(pis));
// once output is resotred, we must terminate
while (true) {
String line = br.readLine();
if (line == null) {
return;
}
downstream.println(line);
userFilter(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
public void terminate() throws InterruptedException, IOException {
restoreDownstream(); // switch back to std
pos.close(); // there will be no more data - signal that
join(); // and wait until capture completes
}
};
Here is an example of using the class:
以下是使用该类的示例：
OutputCaputre outputCapture = new OutputCaputre() {
protected void userFilter(String line) {
downstream.println("Capture: " + line);
}
};
System.out.println("do you see me captured?");
// here is your test
outputCapture.terminate(); // finally, stop capturing
