How to properly add dependency to another plugin: "TestProxy cannot be cast to TestProxy"

Hello,

My plugin needs to depend on some classes (like TestProxy) from com.intellij.execution.junit2. Which is another plugin.
So I add /Applications/IntelliJ IDEA 13 CE.app/plugins/junit/lib/idea-junit.jar as a dependency for my own module (in File -> Project Structure -> ...)


However, for the following piece of code:

public void testSuiteFinished(AbstractTestProxy root) {

     TestProxy junitTest = (TestProxy) root;

}


I get the following exception (which you don't quite see everyday):

java.lang.ClassCastException: com.intellij.execution.junit2.TestProxy cannot be cast to com.intellij.execution.junit2.TestProxy


This is because the class files are loaded by different class loaders. If I print the class loaders I get:

my TestProxy classloader: PluginClassLoader[edu.oregonstate.edu.cope.intellij.recorder, 0.1]

IDEA's TestProxy classloader: PluginClassLoader[JUnit, 1.0]


I also tried adding <depends>JUnit</depends> to my plugin.xml but the same exception gets thrown.


So my question is, how can I depend on a plugin that IDEA also uses? As in depend on the same instance of the plugin.