Bug 327765 EPartService will hide a part of another perspective
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
window.setSelectedElement(stack);
		MPart part = BasicFactoryImpl.eINSTANCE.createPart();
		part.setElementId("partId");
		stack.getChildren().add(part);
		stack.setSelectedElement(part);
		MPartDescriptor descriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		descriptor.setAllowMultiple(true);
		descriptor.setElementId("partId");
		descriptor.setCategory("categoryId");
		application.getDescriptors().add(descriptor);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		MPart shownPart = partService.showPart("partId", PartState.ACTIVATE);
		assertEquals(part, shownPart);
		assertEquals(stack, part.getParent());
	}
	public void testShowPart_Bug318931() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MPartDescriptor partDescriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		partDescriptor.setElementId("partId");
		partDescriptor.setAllowMultiple(true);
		application.getDescriptors().add(partDescriptor);
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);