我有一些方法应该在某些输入上调用 System.exit()。不幸的是，测试这些情况会导致 JUnit 终止!将方法调用放在新线程中似乎没有帮助，因为 System.exit() 会终止 JVM，而不仅仅是当前线程。是否有任何常见的模式来处理这个问题？例如，我可以用 stub 代替 System.exit() 吗？

[编辑] 有问题的类实际上是一个命令行工具，我试图在 JUnit 中对其进行测试。也许 JUnit 根本就不是适合这项工作的工具？欢迎提出补充回归测试工具的建议(最好是与 JUnit 和 EclEmma 很好集成的工具)。

最佳答案

确实，Derkeiler.com建议:

• 为什么要System.exit()？

Instead of terminating with System.exit(whateverValue), why not throw an unchecked exception? In normal use it will drift all the way out to the JVM's last-ditch catcher and shut your script down (unless you decide to catch it somewhere along the way, which might be useful someday).

In the JUnit scenario it will be caught by the JUnit framework, which will report that such-and-such test failed and move smoothly along to the next.

• 防止System.exit()真正退出JVM:

Try modifying the TestCase to run with a security manager that prevents calling System.exit, then catch the SecurityException.

public class NoExitTestCase extends TestCase 
{

    protected static class ExitException extends SecurityException 
    {
        public final int status;
        public ExitException(int status) 
        {
            super("There is no escape!");
            this.status = status;
        }
    }

    private static class NoExitSecurityManager extends SecurityManager 
    {
        @Override
        public void checkPermission(Permission perm) 
        {
            // allow anything.
        }
        @Override
        public void checkPermission(Permission perm, Object context) 
        {
            // allow anything.
        }
        @Override
        public void checkExit(int status) 
        {
            super.checkExit(status);
            throw new ExitException(status);
        }
    }

    @Override
    protected void setUp() throws Exception 
    {
        super.setUp();
        System.setSecurityManager(new NoExitSecurityManager());
    }

    @Override
    protected void tearDown() throws Exception 
    {
        System.setSecurityManager(null); // or save and restore original
        super.tearDown();
    }

    public void testNoExit() throws Exception 
    {
        System.out.println("Printing works");
    }

    public void testExit() throws Exception 
    {
        try 
        {
            System.exit(42);
        } catch (ExitException e) 
        {
            assertEquals("Exit status", 42, e.status);
        }
    }
}

2012 年 12 月更新:

Will建议in the comments使用 System Rules ，一组用于测试使用 java.lang.System 的代码的 JUnit(4.9+) 规则。
Stefan Birkner 最初提到了这一点。 在 his answer 2011 年 12 月。

System.exit(…)

Use the ExpectedSystemExit rule to verify that System.exit(…) is called.
You could verify the exit status, too.

例如:

public void MyTest {
    @Rule
    public final ExpectedSystemExit exit = ExpectedSystemExit.none();

    @Test
    public void noSystemExit() {
        //passes
    }

    @Test
    public void systemExitWithArbitraryStatusCode() {
        exit.expectSystemExit();
        System.exit(0);
    }

    @Test
    public void systemExitWithSelectedStatusCode0() {
        exit.expectSystemExitWithStatus(0);
        System.exit(0);
    }
}

关于Java:如何测试调用 System.exit() 的方法？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/309396/