NoClassDefFoundError: org/testng/TestNG

Question

This error

NoClassDefFoundError: org/testng/TestNG

appears when I'm trying to run my test from Testng.xml file using IntelliJ IDEA. Running my test one by one works perfectly as well as running whole gradle project which points to testng.xml, like grade core-test:test

( On my project I'm using Appium + IntelliJ + TestNG )

But when I'm running testng.xml using IntelliJ I'm immediately getting this message after pressing Run:

Exception in thread "main" java.lang.NoClassDefFoundError: org/testng/TestNG
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.testng.RemoteTestNGStarter.main(RemoteTestNGStarter.java:120)
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:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Caused by: java.lang.ClassNotFoundException: org.testng.TestNG
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 18 more

Answer 1

I found a solution posted here: https://intellij-support.jetbrains.com/hc/en-us/community/posts/206597869-Cannot-launch-NGTest-runner-in-IntelliJ-IDEA-2016-1

I got it to work by selecting "In whole project" (I had "In single module" selected) under the Configuration tab in the TestNG "Run/Debug Configurations."

However, the prior configuration worked in IntelliJ IDEA 15, so to me, it seems that it may have come from a breaking change with newer IDE.

It worked for me.

Answer 2

adding a screenshot to aid Justin's answer above. The default is In single module which needs to be changed to In whole project.