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
public void testPartStack_SetActiveChild6Bug298797() throws Exception {
		MApplication application = MApplicationFactory.eINSTANCE
				.createApplication();
		application.setContext(appContext);
		appContext.set(MApplication.class.getName(), application);
		MWindow window = MApplicationFactory.eINSTANCE.createWindow();
		application.getChildren().add(window);
		MPartStack stack = MApplicationFactory.eINSTANCE.createPartStack();
		window.getChildren().add(stack);
		MPart partA = MApplicationFactory.eINSTANCE.createPart();
		partA.setURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		stack.getChildren().add(partA);
		wb = new E4Workbench(application, appContext);
		wb.createAndRunUI(window);
		CTabFolder tabFolder = (CTabFolder) stack.getWidget();
		assertEquals(0, tabFolder.getSelectionIndex());
		assertEquals(partA, stack.getSelectedElement());
		MPart partB = MApplicationFactory.eINSTANCE.createPart();
		partB.setURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		stack.getChildren().add(partB);
		assertEquals(0, tabFolder.getSelectionIndex());
		assertEquals(partA, stack.getSelectedElement());
		stack.setSelectedElement(partB);
		assertEquals(1, tabFolder.getSelectionIndex());
		assertEquals(partB, stack.getSelectedElement());
	}
	public void testCreateGuiBug301021() throws Exception {
		MApplication application = MApplicationFactory.eINSTANCE
				.createApplication();
		application.setContext(appContext);