当@ Rule的相互依赖时,如何处理它们的排序

Question

我使用在Junit测试用例中运行的嵌入式服务器.有时这些服务器需要一个工作目录(例如Apache Directory服务器).

Junit 4.7中的新@Rule可以处理这些情况.TemporaryFolder-Rule可以创建临时目录.可以为服务器创建自定义ExternalResource-Rule.但是如果我想将结果从一个规则传递到另一个规则,我该如何处理:

import static org.junit.Assert.assertEquals;
import java.io.*;
import org.junit.*;
import org.junit.rules.*;

public class FolderRuleOrderingTest {

    @Rule
    public TemporaryFolder folder = new TemporaryFolder();

    @Rule
    public MyNumberServer server = new MyNumberServer(folder);

    @Test
    public void testMyNumberServer() throws IOException {
        server.storeNumber(10);
        assertEquals(10, server.getNumber());
    }

    /** Simple server that can store one number */
    private static class MyNumberServer extends ExternalResource {

        private TemporaryFolder folder;

        /** The actual datafile where the number are stored */
        private File dataFile;

        public MyNumberServer(TemporaryFolder folder) {
            this.folder = folder;
        }

        @Override
        protected void before() throws Throwable {
            if (folder.getRoot() == null) {
                throw new RuntimeException("TemporaryFolder not properly initialized");
            }

            //All server data are stored to a working folder
            File workingFolder = folder.newFolder("my-work-folder");
            dataFile = new File(workingFolder, "datafile");
        }

        public void storeNumber(int number) throws IOException {
            dataFile.createNewFile();
            DataOutputStream out = new DataOutputStream(new FileOutputStream(dataFile));
            out.writeInt(number);
        }

        public int getNumber() throws IOException {
            DataInputStream in = new DataInputStream(new FileInputStream(dataFile));
            return in.readInt();
        }
    }
}

在此代码中,文件夹作为参数发送到服务器,以便服务器可以创建工作目录来存储数据.但是这不起作用,因为Junit按照与文件中定义的规则相反的顺序处理规则.TemporaryFolder规则不会在服务器规则之前执行.因此,TempraryFolder中的根文件夹将为null,从而导致相对于当前工作目录创建任何文件.

如果我颠倒了我的类中的属性的顺序,我得到一个编译错误,因为我无法在定义之前引用变量.

我正在使用Junit 4.8.1(因为4.7版本中的规则排序有点固定)

Answer 1

编辑:使用最近发布的Junit 4.10,您可以使用@RuleChain正确地链接规则(参见最后).

您可以在没有@Rule注释的情况下引入另一个私有字段,然后您可以根据需要重新排序代码:

public class FolderRuleOrderingTest {

    private TemporaryFolder privateFolder = new TemporaryFolder();

    @Rule
    public MyNumberServer server = new MyNumberServer(privateFolder);

    @Rule
    public TemporaryFolder folder = privateFolder;

    @Test
    public void testMyNumberServer() throws IOException {
        server.storeNumber(10);
        assertEquals(10, server.getNumber());
    }
    ...
}

最干净的解决方案是有一个复合规则,但上述应该有效.

编辑:使用最近发布的Junit 4.10,您可以使用RuleChain正确链接规则:

public static class UseRuleChain {
   @Rule
   public TestRule chain= RuleChain
                          .outerRule(new LoggingRule("outer rule"))
                          .around(new LoggingRule("middle rule"))
                          .around(new LoggingRule("inner rule"));

   @Test
   public void example() {
           assertTrue(true);
   }
}

写日志

starting outer rule
starting middle rule
starting inner rule
finished inner rule
finished middle rule
finished outer rule

Answer 2

要使规则依赖,您必须首先初始化它们并使用构造函数或(根据您的规则)流畅的构建器创建依赖关系.必须在字段初始化中定义依赖关系,并且不能在@Before方法中创建依赖关系,因为这些在规则应用之后执行.要强制正确排序规则,必须定义规则链.

public class FolderRuleOrderingTest {

  private TemporaryFolder folder = new TemporaryFolder();
  //assume, we have a rule that creates a testfile in a temporary folder
  //we create a dependency relationship between file and folder,
  //so that file depends on folder
  private TemporaryFile file = new TemporaryFile(folder, "testfile.txt");

  //the rule chain ensures, the temporary folder is created before and removed 
  //after the testfile has been created and deleted (or whatever)
  @Rule
  public RuleChain chain= RuleChain.outerRule(folder).around(file));


  @Test
  public void testFileExist() throws IOException {
    assertTrue(file.getFile().exist());
  }
  ...
}

Answer 3

如果您找不到正常的解决方案，您始终可以创建@Rule包含所有其他规则的复合规则（也是唯一一个带有注释的规则）并按顺序执行它们。