How does JUnit find the eclipse plug-in being tested?

Question

I am writing a plug-in (ClassRefactoringPlugin) that examines source code in Eclipse 3.5.2. The plug-in contains a CallData class that examines a Java source file and figures out which Java elements are called from a method using JDT operations. I wrote a JUnit 4 test for this class that also resides in the ClassRefactoringPlugin project. When I ran it as a JUnit plug-in test, I got:

Java Model Exception: Java Model Status [ClassRefactoringPlugin does not exist]

What have I done wrong? The configuration specifies to launch with all workspace and enabled target plug-ins, and ClassRefactoringPlugin is in my dropins directory. (Although shouldn't the project's version of the plug-in be recognized by the spawned workspace?)

Here's the stack trace:

junit.framework.AssertionFailedError: ClassRefactoringPlugin does not exist
    at junit.framework.Assert.fail(Assert.java:47)
    at nz.ac.vuw.ecs.kcassell.callgraph.CallDataTest.testCollectCallData(CallDataTest.java:60)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:73)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:46)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:180)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:41)
    at org.junit.runners.ParentRunner$1.evaluate(ParentRunner.java:173)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:220)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:46)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.pde.internal.junit.runtime.RemotePluginTestRunner.main(RemotePluginTestRunner.java:62)
    at org.eclipse.pde.internal.junit.runtime.UITestApplication$1.run(UITestApplication.java:114)
    at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
    at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:134)
    at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3468)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3115)
    at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2405)
    at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2369)
    at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2221)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:500)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:493)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
    at org.eclipse.pde.internal.junit.runtime.UITestApplication.start(UITestApplication.java:46)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:194)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:368)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:559)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1311)
    at org.eclipse.equinox.launcher.Main.main(Main.java:1287)

I am new to plug-in development, so any help would be much appreciated.

Cheers, Keith