Scala:如何测试调用System.exit()的方法？

Question

我一直在开发一个命令行工具,它在某些输入上调用System.exit()(不想使用异常而不是).

我熟悉Java:如何测试调用System.exit()的方法？它是最优雅的方法.

不幸的是,它是不够纯,因为我不得不添加的依赖关系到系统的规则,JUnit的接口

System.exit在specs2中是否有任何常见的处理模式,这种模式比我目前使用specs2的方法更纯粹？

import org.junit.Rule;
import org.junit.Test;
import org.junit.contrib.java.lang.system.ExpectedSystemExit;

public class ConverterTest {
    @Rule
    public final ExpectedSystemExit exit = ExpectedSystemExit.none();

    @Test
    public void emptyArgs() {
        exit.expectSystemExit();
        Converter.main(new String[]{});
    }

    @Test
    public void missingOutArgument() {
        exit.expectSystemExitWithStatus(1);
        Converter.main(new String[]{"--in", "src/test/resources/078.xml.gz"});
    }
}

Answer 1

如果你真的希望使用一个方法System.exit(),最简单的测试方法实际上就是调用它来替换你在调用时SecurityManager抛出ExitException(子类SecurityException)的System.exit()方法:

class SystemExitSpec

import java.security.Permission

import org.specs2.mutable.Specification
import org.specs2.specification.BeforeAfterAll

sealed case class ExitException(status: Int) extends SecurityException("System.exit() is not allowed") {
}

sealed class NoExitSecurityManager extends SecurityManager {
  override def checkPermission(perm: Permission): Unit = {}

  override def checkPermission(perm: Permission, context: Object): Unit = {}

  override def checkExit(status: Int): Unit = {
    super.checkExit(status)
    throw ExitException(status)
  }
}


abstract class SystemExitSpec extends Specification with BeforeAfterAll {

  sequential

  override def beforeAll(): Unit = System.setSecurityManager(new NoExitSecurityManager())

  override def afterAll(): Unit = System.setSecurityManager(null)
}

测试ConverterSpec

import org.specs2.execute.Failure

import scala.io.Source

class ConverterSpec extends SystemExitSpec {

"ConverterSpec" should {

    "empty args" >> {
      try {
        Converter.main(Array[String]())
        Failure("shouldn't read this code")
      } catch {
        case e: ExitException =>
          e.status must_== 1
      }
      1 must_== 1
    }
}