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
partStack.getChildren().add(placeholderC);
		partStack.setSelectedElement(placeholderC);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		assertNull(partB.getObject());
		EPartService partService = window.getContext().get(EPartService.class);
		partService.activate(partA);
		partService.hidePart(partA);
		assertEquals(partC, partService.getActivePart());
	}
	public void testHidePart_ActivationHistory19() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPart partD = BasicFactoryImpl.eINSTANCE.createPart();
		window.getSharedElements().add(partD);
		MPerspectiveStack perspectiveStack = AdvancedFactoryImpl.eINSTANCE
				.createPerspectiveStack();
		window.getChildren().add(perspectiveStack);
		window.setSelectedElement(perspectiveStack);
		MPerspective perspectiveA = AdvancedFactoryImpl.eINSTANCE
				.createPerspective();
		perspectiveStack.getChildren().add(perspectiveA);
		perspectiveStack.setSelectedElement(perspectiveA);
		MPlaceholder placeholderD1 = AdvancedFactoryImpl.eINSTANCE
				.createPlaceholder();
		placeholderD1.setRef(partD);
		partD.setCurSharedRef(placeholderD1);