We copied TestableObject and ITestHarness into
org.eclipse.e4.ui.workbench3, but kept the copies in
org.eclipse.ui.workbench.  This could lead to LinkageErrors depending
on the load order of e4.ui.workbench3 and ui.workbench.

A reproducible test case seems to be the MyFirstTest from their
EclipseCon 2009 example with SWTBot 2.5.0
<http://wiki.eclipse.org/SWTBot/UsersGuide#Getting_started_with_SWTBot_for_Eclipse_Plugins>