Win 2000 SP2, JDK 1.4.1_01, S1S4u1 EE (also happens in
netBeans)

IDE either fails with assertion exception (and locks-up)
or simply locks-up.
1) Follow http://junit.netbeans.org/JUnit_tutorial.html
2) Open any of the ...Test classes
3) Create breakpoint
4) Debug root test class.
Voila!

Assertion exception is NOT written into ide.log and looks
like this:

"...
Time: 0.078
There was 1 failure:
1)testGreeting2(HelloWorldTest)
junit.framework.AssertioFailedException: expected:<Hello
world!> but was:<Good bye>
at HelloWorldTest.testGreeting2
(HelloWorldTest.java:46)
at sun.reflect.NativeMethodAccessorImpl.invoke0
(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke
(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegationMethodAccessorImpl.invoke
(DelegatingMethodAccessorImpl.java:25)
at org.netbeans.junit.NbTestCase.run
(NbTestCase.java:76)
at RootSuite.main(RootSuite.java:22)

FAILURES!!!
Tests run: 3, Failures: 1, Errors: 0"

IDE is responsive ~0.5 seconds after the execption appears, then locks up.
For JVM stacktrace see attachment.