Bug 328946 Part activation history may return incorrect candidate if no placeholders could be found in a perspective
1. Window > Open Perspective > Other... > CVS Repository Exploring 2. Hide the 'CVS Repositories' view. 3. The 'History' view should become active, it is not.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		partService.activate(partA);
		assertEquals(partA, partService.getActivePart());
		MPart partB = partService.showPart("partB",
				EPartService.PartState.CREATE);
		assertEquals(2, partStack.getChildren().size());
		assertEquals(
				"Only creating the part, the active part should not have changed",
				partA, partService.getActivePart());
		assertNotNull("The shown part should have a context",
				partB.getContext());
		assertFalse(partService.isPartVisible(partB));
	}
	public void testShowPart_Id_CREATE3() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		MPartDescriptor partDescriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		partDescriptor.setElementId("partB");
		partDescriptor.setCategory("aCategory");
		application.getDescriptors().add(partDescriptor);
		MPartStack partStackA = BasicFactoryImpl.eINSTANCE.createPartStack();
		window.getChildren().add(partStackA);
		MPartStack partStackB = BasicFactoryImpl.eINSTANCE.createPartStack();
		partStackB.getTags().add("aCategory");
		window.getChildren().add(partStackB);