报错：
二月 07, 2022 9:59:52 下午 org.junit.platform.launcher.core.DefaultLauncher handleThrowable
警告: TestEngine with ID ‘junit-jupiter’ failed to discover tests
java.lang.NoClassDefFoundError: org/junit/platform/engine/support/discovery/SelectorResolver
at org.junit.jupiter.engine.JupiterTestEngine.discover(JupiterTestEngine.java:69)
at org.junit.platform.launcher.core.DefaultLauncher.discoverEngineRoot(DefaultLauncher.java:168)
at org.junit.platform.launcher.core.DefaultLauncher.discoverRoot(DefaultLauncher.java:155)
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128)
at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
at com.intellij.rt.junit.IdeaTestRunner
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Repeater.startRunnerWithArgs(IdeaTestRunner.java:33) at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235) at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54) Caused by: java.lang.ClassNotFoundException: org.junit.platform.engine.support.discovery.SelectorResolver at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher
Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)atcom.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)atcom.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)Causedby:java.lang.ClassNotFoundException:org.junit.platform.engine.support.discovery.SelectorResolveratjava.net.URLClassLoader.findClass(URLClassLoader.java:381)atjava.lang.ClassLoader.loadClass(ClassLoader.java:424)atsun.misc.LauncherAppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
… 8 more
解决方法：
1、Idea插件-Maven helper插件，找到所有冲突，选中红色的exclude掉。还是一样，没解决。
2、运行mvn dependency::tree，仔细看一遍没看出问题。
3、运行mvn help:effective-pom，得到最终的Maven文件结构。搜索文本 junit-jupiter-api（还有junit-jupiter-engine等），发现出现2个不同版本的（pom文件里是5.8.2，但是里面出来一个 5.3.2），换成5.3.2则没有报错了
出现原因：
不明确，之前没有加Springboot，单元测试还是正常的。又加了个springboot玩一下，再跑单元测试就突然报这个错误。