场景复现
在idea上鼓捣半天发现单测一直报"没有发现测试"：
Internal Error occurred. org.junit.platform.commons.JUnitException: TestEngine with ID 'junit-jupiter' failed to discover tests at org.junit.platform.launcher.core.EngineDiscoveryOrchestrator.discoverEngineRoot(EngineDiscoveryOrchestrator.java:160) at org.junit.platform.launcher.core.EngineDiscoveryOrchestrator.discoverSafely(EngineDiscoveryOrchestrator.java:134) at org.junit.platform.launcher.core.EngineDiscoveryOrchestrator.discover(EngineDiscoveryOrchestrator.java:108) at org.junit.platform.launcher.core.EngineDiscoveryOrchestrator.discover(EngineDiscoveryOrchestrator.java:80) at org.junit.platform.launcher.core.DefaultLauncher.discover(DefaultLauncher.java:110) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:86) at org.junit.platform.launcher.core.DefaultLauncherSession$DelegatingLauncher.execute(DefaultLauncherSession.java:86) at org.junit.platform.launcher.core.SessionPerRequestLauncher.execute(SessionPerRequestLauncher.java:53) at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71) at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33) at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220) at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53) Caused by: org.junit.platform.commons.JUnitException: MethodSelector [className = 'com.kalar.idea.junitStudy.hello', methodName = 'testSayHi', methodParameterTypes = ''] resolution failed at org.junit.platform.launcher.listeners.discovery.AbortOnFailureLauncherDiscoveryListener.selectorProcessed(AbortOnFailureLauncherDiscoveryListener.java:39) at org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolution.resolveCompletely(EngineDiscoveryRequestResolution.java:102) at org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolution.run(EngineDiscoveryRequestResolution.java:82) at org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolver.resolve(EngineDiscoveryRequestResolver.java:113) at org.junit.jupiter.engine.discovery.DiscoverySelectorResolver.resolveSelectors(DiscoverySelectorResolver.java:46) at org.junit.jupiter.engine.JupiterTestEngine.discover(JupiterTestEngine.java:69) at org.junit.platform.launcher.core.EngineDiscoveryOrchestrator.discoverEngineRoot(EngineDiscoveryOrchestrator.java:152) ... 11 more Caused by: org.junit.platform.commons.PreconditionViolationException: Could not load class with name: com.kalar.idea.junitStudy.hello at org.junit.platform.engine.discovery.MethodSelector.lambda$lazyLoadJavaClass$0(MethodSelector.java:157) at org.junit.platform.commons.function.Try$Failure.getOrThrow(Try.java:335) at org.junit.platform.engine.discovery.MethodSelector.lazyLoadJavaClass(MethodSelector.java:156) at org.junit.platform.engine.discovery.MethodSelector.getJavaClass(MethodSelector.java:135) at org.junit.jupiter.engine.discovery.MethodSelectorResolver.resolve(MethodSelectorResolver.java:73) at org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolution.lambda$resolve$2(EngineDiscoveryRequestResolution.java:146) at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) at java.util.ArrayList$ArrayListSpliterator.tryAdvance(ArrayList.java:1359) at java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:126) at java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:498) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:485) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) at java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:464) at org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolution.resolve(EngineDiscoveryRequestResolution.java:185) at org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolution.resolve(EngineDiscoveryRequestResolution.java:125) at org.junit.platform.engine.support.discovery.EngineDiscoveryRequestResolution.resolveCompletely(EngineDiscoveryRequestResolution.java:91) ... 16 more Caused by: java.lang.ClassNotFoundException: com.kalar.idea.junitStudy.hello at java.net.URLClassLoader.findClass(URLClassLoader.java:382) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) at org.junit.platform.commons.util.ReflectionUtils.lambda$tryToLoadClass$9(ReflectionUtils.java:829) at org.junit.platform.commons.function.Try.lambda$call$0(Try.java:57) at org.junit.platform.commons.function.Try.of(Try.java:93) at org.junit.platform.commons.function.Try.call(Try.java:57) at org.junit.platform.commons.util.ReflectionUtils.tryToLoadClass(ReflectionUtils.java:792) at org.junit.platform.commons.util.ReflectionUtils.tryToLoadClass(ReflectionUtils.java:748) ... 32 more 进程已结束，退出代码为 -2
代码也没什么问题
package com.kalar.idea.junitStudy;
import org.junit.jupiter.api.Test;
public class hello {
@Test
public void testSayHi() {
System.out.println("Hi Junit.");
}
}
看一下目录结构
总之就很奇怪
直到我突发奇想。。。
这个东西怎么不讲武德的？没有拓展名？
于是我当场加上拓展名，测试愉快的通过了。
经过五分钟的排查后找到了原因：
原来是我在新建测试类时，选择了新建文件，然后关联了文件类型，如图：
然后复制粘贴一下hellotest的代码
不能说毫无差别，简直一模一样，谁能想到这是个缺失拓展名的测试类呢？
（没用的知识增加了！）
