PreconditionViolationException: Could not load class with name: testing.ConnectionTest

Question

When I try to run my Junit tests, I am getting this error. How can I fix it to run my tests? I have included Junit 4 in my lib folder.

/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/bin/java -ea -Didea.launcher.port=7538 "-Didea.launcher.bin.path=/Applications/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath "/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_60.jdk/Contents/Home/lib/tools.jar:/Users/yf/Desktop/sl/419/ece419/BasicStorageServer-stub/gson-1.1.jar:/Users/yf/Desktop/sl/419/ece419/BasicStorageServer-stub/libs/log4j-1.2.17.jar:/Applications/IntelliJ IDEA.app/Contents/lib/junit.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-jupiter-api-5.0.0-M3.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/opentest4j-1.0.0-M1.jar:/Applications/IntelliJ IDEA.app/Contents/lib/junit-4.12.jar:/Applications/IntelliJ IDEA.app/Contents/lib/hamcrest-core-1.3.jar:/Users/yf/Desktop/sl/419/ece419/BasicStorageServer-stub/libs/gson-2.8.0.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit5-rt.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-platform-launcher-1.0.0-M3.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-jupiter-engine-5.0.0-M3.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-platform-commons-1.0.0-M3.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-platform-engine-1.0.0-M3.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-platform-runner-1.0.0-M3.jar:/Applications/IntelliJ IDEA.app/Contents/plugins/junit/lib/junit-vintage-engine-4.12.0-M3.jar" com.intellij.rt.execution.application.AppMain com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit5 testing.ConnectionTest
Jan 28, 2017 1:01:49 AM org.junit.platform.launcher.core.ServiceLoaderTestEngineRegistry loadTestEngines
INFO: Discovered TestEngines with IDs: [junit-jupiter, junit-vintage]
Internal Error occurred.
org.junit.platform.commons.util.PreconditionViolationException: Could not load class with name: testing.ConnectionTest
    at org.junit.platform.engine.discovery.ClassSelector.lambda$getJavaClass$0(ClassSelector.java:71)
    at java.util.Optional.orElseThrow(Optional.java:290)
    at org.junit.platform.engine.discovery.ClassSelector.getJavaClass(ClassSelector.java:70)
    at org.junit.jupiter.engine.discovery.DiscoverySelectorResolver.lambda$resolveSelectors$2(DiscoverySelectorResolver.java:60)
    at java.util.ArrayList.forEach(ArrayList.java:1249)
    at org.junit.jupiter.engine.discovery.DiscoverySelectorResolver.resolveSelectors(DiscoverySelectorResolver.java:59)
    at org.junit.jupiter.engine.JupiterTestEngine.resolveDiscoveryRequest(JupiterTestEngine.java:50)
    at org.junit.jupiter.engine.JupiterTestEngine.discover(JupiterTestEngine.java:43)
    at org.junit.platform.launcher.core.DefaultLauncher.discoverRoot(DefaultLauncher.java:109)
    at org.junit.platform.launcher.core.DefaultLauncher.discover(DefaultLauncher.java:79)
    at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:237)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Solution

The exception is thrown from ClassSelector class line 71 which would try to load the class with the name specified by your code.

That said, the class name testing.ConnectionTest seems suspicious at the first look which is why you get that exception.

You might be intending to specify ConnectionTest.class.