java.lang.NoClassDefFoundError in junit

1. Right click your project in Package Explorer > click Properties
2. go to Java Build Path > Libraries tab
3. click on 'Add Library' button
4. select JUnit
5. click Next.
6. select in dropdown button JUnit4 or other new versions.
7. click finish.
8. Then Ok.

1. Eclipse -> Top menu -> Run -> Run Configurations
2. Delete all the occurrences of your test. Your test may appear as YourTest.Method_1(). Delete that as well.
3. Re-run. Let Eclipse build a fresh configuration.

Addendum: Locally I have created a "User Library" and added to my projects which has

hamcrest-core-1.3.jar

junit-4.12.jar

The same problem can occur if you have downloaded JUnit jar from the JUnit website, but forgotten to download the Hamcrest jar - both are required (the instructions say to download both, but I skipped ahead! Oops)

When using in Maven, update artifact junit:junit from e.g. 4.8.2 to 4.11.

On Eclipse I was able to solve the above issue by following the below steps :

Right-click on the test file which you want to run, Select Run As -> Run Configurations -> Select Classpath tab -> Select to the bootstrap Entries -> Select Advanced -> Select Add library -> Select JUnit -> Next ->Select JUnit4 from the drop-down -> Finish

Then Select Apply -> Run