Bug 304211 StackRenderer does not set eagerly created controls to the item
Right-clicking on a Java element and then using 'Open Declaration' opens an editor on the specified file but its content is not shown. Switching tabs or selecting items in the 'Outline' view does _not_ help. Seems to be calling IWorkbenchPage's APIs properly. No idea yet as to what's going on over here.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java
stack.setSelectedElement(partA);
		wb = new E4Workbench(application, appContext);
		wb.createAndRunUI(window);
		CTabFolder tabFolder = (CTabFolder) stack.getWidget();
		assertEquals(0, tabFolder.getSelectionIndex());
		EPartService service = (EPartService) window.getContext().get(
				EPartService.class.getName());
		service.showPart(partB.getId(), PartState.ACTIVATE);
		assertEquals("Showing a part should alter the tab folder's selection",
				1, tabFolder.getSelectionIndex());
	}
	public void testPartStack_SetActiveChild3Bug299379() throws Exception {
		MApplication application = MApplicationFactory.eINSTANCE
				.createApplication();
		application.setContext(appContext);
		appContext.set(MApplication.class.getName(), application);
		MPartDescriptor descriptor = MApplicationFactory.eINSTANCE
				.createPartDescriptor();
		descriptor
				.setURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		descriptor.setId("part");
		descriptor.setCategory("aStack");
		application.getDescriptors().add(descriptor);
		MWindow window = MApplicationFactory.eINSTANCE.createWindow();
		application.getChildren().add(window);
		MPartStack stack = MApplicationFactory.eINSTANCE.createPartStack();
		stack.setId("aStack");
		window.getChildren().add(stack);
		wb = new E4Workbench(application, appContext);
		wb.createAndRunUI(window);