Bug 322356 EPS's isPartVisible(MPart) method does not consider placeholders
SSIA
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
application.getDescriptors().add(partDescriptor);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		assertNull(partService.showPart("partId2", partState));
	}
	public void testShowPart_Id_IncorrectDescriptor_ACTIVATE() {
		testShowPart_Id_IncorrectDescriptor(PartState.ACTIVATE);
	}
	public void testShowPart_Id_IncorrectDescriptor_VISIBLE() {
		testShowPart_Id_IncorrectDescriptor(PartState.VISIBLE);
	}
	public void testShowPart_Id_IncorrectDescriptor_CREATE() {
		testShowPart_Id_IncorrectDescriptor(PartState.CREATE);
	}
	private void testShowPart_Id_MultipleExists(boolean multipleAllowed,
			PartState partState) {
		MApplication application = createApplication("partId");
		MWindow window = application.getChildren().get(0);
		MPartStack stack = (MPartStack) window.getChildren().get(0);
		MPart part = (MPart) stack.getChildren().get(0);
		MPartDescriptor partDescriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		partDescriptor.setAllowMultiple(multipleAllowed);
		partDescriptor.setElementId("partId");
		application.getDescriptors().add(partDescriptor);
		stack.setSelectedElement(part);
		window.setSelectedElement(stack);
		application.setSelectedElement(window);
		getEngine().createGui(window);