Bug 334559 EPartService's part searching path may not include parts outside of the active perspective
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
MPartStack partStackB = (MPartStack) windowB.getChildren().get(0);
		MPart partFrontB = (MPart) partStackB.getChildren().get(0);
		MPart partBackB = (MPart) partStackB.getChildren().get(1);
		partStackB.setSelectedElement(partFrontB);
		getEngine().createGui(windowA);
		getEngine().createGui(windowB);
		EPartService partServiceA = (EPartService) partFrontA.getContext().get(
				EPartService.class.getName());
		EPartService partServiceB = (EPartService) partFrontB.getContext().get(
				EPartService.class.getName());
		assertTrue(partServiceA.isPartVisible(partFrontA));
		assertFalse(partServiceA.isPartVisible(partBackA));
		assertFalse(partServiceA.isPartVisible(partFrontB));
		assertFalse(partServiceA.isPartVisible(partBackB));
		assertFalse(partServiceB.isPartVisible(partFrontA));
		assertFalse(partServiceB.isPartVisible(partBackA));
		assertTrue(partServiceB.isPartVisible(partFrontB));
		assertFalse(partServiceB.isPartVisible(partBackB));
	}
	public void testIsPartVisible_Placeholder() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MPartDescriptor partDescriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		partDescriptor.setCategory("containerTag");
		partDescriptor.setElementId("partId");
		partDescriptor.setAllowMultiple(true);
		application.getDescriptors().add(partDescriptor);
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);