JUnit：如何模拟System.in测试？ [英] JUnit: How to simulate System.in testing?

问题描述

我有一个Java命令行程序。我想创建JUnit测试用例，以便能够模拟 System.in 。因为当我的程序运行它将进入while循环并等待用户的输入。如何在JUnit中模拟？

I have a Java command-line program. I would like to create JUnit test case to be able to simulate System.in. Because when my program runs it will get into the while loop and waits for input from users. How do I simulate that in JUnit?

感谢

推荐答案

在技​​术上可以切换 System.in ，但一般来说，它更强大，不直接在你的代码中调用它，但添加一个间接层，所以输入源是从应用程序中的一个点控制的。确切地说，你如何做到这一点是一个实现细节 - 依赖注入的建议是好的，但你不一定需要引入第三方框架;你可以从调用代码传递一个I / O上下文。

It is technically possible to switch System.in, but in general, it would be more robust not to call it directly in your code, but add a layer of indirection so the input source is controlled from one point in your application. Exactly how you do that is an implementation detail - the suggestions of dependency injection are fine, but you don't necessarily need to introduce 3rd party frameworks; you could pass round an I/O context from the calling code, for example.

如何切换 System.in ：

String data = "Hello, World!\r\n";
InputStream stdin = System.in;
try {
  System.setIn(new ByteArrayInputStream(data.getBytes()));
  Scanner scanner = new Scanner(System.in);
  System.out.println(scanner.nextLine());
} finally {
  System.setIn(stdin);
}

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