Java 8升级至Java 11后JUnit 4行为异常原因咨询

环境信息 #

• Gradle版本：4.10.3

> gradlew -version
------------------------------------------------------------
Gradle 4.10.3
------------------------------------------------------------

Build time:   2018-12-05 00:50:54 UTC
Revision:     e76905e3a1034e6f724566aeb985621347ff43bc

Kotlin DSL:   1.0-rc-6
Kotlin:       1.2.61
Groovy:       2.4.15
Ant:          Apache Ant(TM) version 1.9.11 compiled on March 23 2018
JVM:          11.0.20 (Azul Systems, Inc. 11.0.20+8-LTS)
OS:           Windows 10 10.0 amd64

• JUnit版本：4.13.2

问题背景 #

仅将JDK/JRE从Java 8升级至Java 11，JUnit与Gradle版本未做任何改动，此前在Java 8环境下运行完全正常。

项目包含两类测试：

• 随构建流程自动运行的单元测试
• 通过可选Gradle任务触发的集成测试

项目中存在一批仅用于测试场景的工具类，具体情况：

• 多数为私有内部类，部分还实现了私有接口
• 部分是供多个测试类调用的公共类，但本身并非测试类
• 部分类依赖重载构造方法实现核心功能

升级后出现的异常行为 #

升级到Java 11后，JUnit开始将所有这类工具类（甚至包括枚举和接口）错误识别为测试类，并抛出三类错误：

1. 私有类不符合测试类需为公共类的要求
2. 类中不存在可运行的@Test方法
3. 部分类未满足测试类需有唯一构造方法的规则

为所有工具类（包括枚举、接口）添加@Ignore注解可以规避该问题，但无法理解为何仅升级Java版本就会导致JUnit的行为发生如此明显的变化。

错误示例（私有接口触发的集成测试失败） #

org.junit.runners.model.InvalidTestClassError: Invalid test class 'com.XXX.YYY.integration.support.UserManager$UserManagerOperations':
  1. The class com.XXX.YYY.integration.support.UserManager$UserManagerOperations is not public.
  2. Test class should have exactly one public constructor
  3. No runnable methods
    at org.junit.runners.ParentRunner.validate(ParentRunner.java:525)
    at org.junit.runners.ParentRunner.<init>(ParentRunner.java:102)
    at org.junit.runners.BlockJUnit4ClassRunner.<init>(BlockJUnit4ClassRunner.java:84)
    at org.junit.runners.JUnit4.<init>(JUnit4.java:23)
    at org.junit.internal.builders.JUnit4Builder.runnerForClass(JUnit4Builder.java:10)
    at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:70)
    at org.junit.internal.builders.AllDefaultPossibilitiesBuilder.runnerForClass(AllDefaultPossibilitiesBuilder.java:37)
    at org.junit.runners.model.RunnerBuilder.safeRunnerForClass(RunnerBuilder.java:70)
    at org.junit.internal.requests.ClassRequest.createRunner(ClassRequest.java:28)
    at org.junit.internal.requests.MemoizingRequest.getRunner(MemoizingRequest.java:19)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.runTestClass(JUnitTestClassExecutor.java:78)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:58)
    at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:38)
    at org.gradle.api.internal.tasks.testing.junit.AbstractJUnitTestClassProcessor.processTestClass(AbstractJUnitTestClassProcessor.java:66)
    at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:51)
    at jdk.internal.reflect.GeneratedMethodAccessor14.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32)
    at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93)
    at com.sun.proxy.$Proxy2.processTestClass(Unknown Source)
    at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:117)
    at jdk.internal.reflect.GeneratedMethodAccessor13.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
    at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
    at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:155)
    at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:137)
    at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:404)
    at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
    at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
    at java.base/java.lang.Thread.run(Thread.java:829)

核心疑问 #

已有临时解决方案，现寻求以下问题的答案：

1. 为何未改动JUnit版本，其行为却随Java版本升级发生变化？
2. 这种行为变更的逻辑依据是什么？

（注：未来计划升级Gradle版本并迁移至JUnit 5，但由于当前代码库规模较大，需采用小步迭代的方式推进，因此优先需要理解该问题背后的原因）

内容的提问来源于stack exchange，提问作者franklyspeaking