@Rule声明在调试尝试时导致错误

Question

一个groovy JUnit测试类只有一个静态声明:

@Rule
public static ErrorCollector errorCollector;

尝试在调试模式下启动测试后，引发异常:

java.lang.NullPointerException
at org.junit.runners.BlockJUnit4ClassRunner.withRules(BlockJUnit4ClassRunner.java:354)
at org.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:270)
at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

异常在代码中的任何一行开始之前引发。如果我扔掉"@Rule"这个词，测试运行正常(至少从一开始)

进口:

import static org.hamcrest.CoreMatchers.*;
import org.hamcrest.Matcher;
import static org.hamcrest.Matchers.*;
import org.junit.Rule;
import org.junit.rules.ErrorCollector;
import org.junit.Test;
import static org.junit.Assert.*;
import org.junit.Before;
import groovy.util.slurpersupport.NodeChild
import groovy.xml.MarkupBuilder
import groovy.xml.StreamingMarkupBuilder
import groovy.xml.XmlUtil
import org.codehaus.groovy.tools.xml.DomToGroovy
import org.joda.time.DateTime
import org.w3c.dom.Document;
import java.util.concurrent.Callable;

JUnit version 4.8.2

Eclipse version: 3.6

Java版本:1.6.41

请问我应该在哪里找问题?

Answer 1

在ErrorCollector javadoc中可以看到，必须创建一个实例来使用它，如下所示:

    @Rule
    public ErrorCollector collector= new ErrorCollector();

Answer 2

这似乎是Runner的一个bug:

//Correct variants:
@Rule
public ErrorCollector collector1= new ErrorCollector();

public ErrorCollector collector2= null;
@Rule
collector2= new ErrorCollector();
public ErrorCollector collector3;
@Rule
collector3= new ErrorCollector();

// incorrect variants:
@Rule
public ErrorCollector collector4= null;
@Rule
public ErrorCollector collector5;
@Rule
public ErrorCollector collector5=somethingThatIsNotRule;
@Rule
public ErrorCollector collector5=anotherRule;
//BUT:
//the runner takes the following, and runs it without problems, too:
public ErrorCollector collector6= null;
{
  @Rule
  collector6= null;
}

因此，运行程序在构造测试之前进行了过多的检查。