Bug 326087 StackRenderer arbitrarily changes selected element when MPartStack is being unrendered
1. Open two files. 2. Activate the editor in the back. 3. Restart 4. The file in the wrong is active now. :O
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java
CTabFolder tabFolder = (CTabFolder) stack.getWidget();
		assertNull(part.getWidget());
		assertNull(part.getRenderer());
		assertNull(part.getObject());
		assertEquals(0, tabFolder.getItemCount());
	}
	public void testCTabItem_SetControl_Bug304211() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		application.setContext(appContext);
		appContext.set(MApplication.class.getName(), application);
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		MPartStack stack = BasicFactoryImpl.eINSTANCE.createPartStack();
		window.getChildren().add(stack);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		partA.setElementId("partA");
		partA.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		stack.getChildren().add(partA);
		stack.setSelectedElement(partA);
		wb = new E4Workbench(application, appContext);
		wb.createAndRunUI(window);
		IPresentationEngine engine = (IPresentationEngine) appContext
				.get(IPresentationEngine.class.getName());
		CTabFolder folder = (CTabFolder) stack.getWidget();
		CTabItem itemA = folder.getItem(0);
		assertEquals(
				"The presentation engine should have created the part and set it",
				partA.getWidget(), itemA.getControl());
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();