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
partB.setElementId("partB");
		partB.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		
		stack.getChildren().add(partB);
		CTabItem item2 = folder.getItem(1);
		assertNull(
				"For a stack, the object will not be rendered unless explicitly required",
				item2.getControl());
		
		engine.createGui(partB);
		assertEquals(
				"The presentation engine should have created the part and set it",
				partB.getWidget(), item2.getControl());
		
		stack.setSelectedElement(partB);
		assertEquals("Selecting the element should not have changed anything",
				partB.getWidget(), item2.getControl());
	}
	public void testToBeRenderedCausesSelectionChanges() {
		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");