Bug 326300 EPartService's activate(MPart) method may not work if you activate the window's active part
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
partSashContainer.setSelectedElement(partStack);
		MPart part = BasicFactoryImpl.eINSTANCE.createPart();
		part.setElementId("partId");
		part.setToBeRendered(false);
		partStack.getChildren().add(part);
		partStack.setSelectedElement(part);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		MPart shownPart = partService.showPart("partId", partState);
		assertEquals(1, partStack.getChildren().size());
		assertEquals(part, partStack.getChildren().get(0));
		assertEquals(part, shownPart);
		assertTrue("A shown part should be rendered", part.isToBeRendered());
	}
	public void testShowPart_Id_Unrendered_CREATE3() {
		testShowPart_Id_Unrendered3(PartState.CREATE);
	}
	public void testShowPart_Id_Unrendered_VISIBLE3() {
		testShowPart_Id_Unrendered3(PartState.VISIBLE);
	}
	public void testShowPart_Id_Unrendered_ACTIVATE3() {
		testShowPart_Id_Unrendered3(PartState.ACTIVATE);
	}
	private void testShowPart_Id_PartAlreadyShown(PartState partState) {
		MApplication application = createApplication(1, new String[1][0]);
		MWindow window = application.getChildren().get(0);
		MPartDescriptor partDescriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();