Below are the installation steps for installing JUnit:
unzip the file
add junit.jar to the CLASSPATH. For example: set classpath=%classpath%;INSTALL_DIR\junit3\junit.jar
test the installation by using either the batch or the graphical TestRunner tool to run the tests that come with this release. All the tests should pass OK.
for the batch TestRunner type:
    java junit.textui.TestRunner junit.samples.AllTests
for the graphical TestRunner type:
    java junit.awtui.TestRunner junit.samples.AllTests
for the Swing based graphical TestRunner type:
    java junit.swingui.TestRunner junit.samples.AllTests

after doing the above

I get the error as Exception in thread "main" java.lang.NoclassDefFoundError :junit/swinggui/Testrunnner