Bug 326177 EPartService's getActivePart() does not appear to work properly for an application with multiple windows
Based on the code in PartServiceCreationFunction, the EPartService implementation being returned when an application's context is queried seems to be a window-level EPartService implementation.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		MPart saveablePart = BasicFactoryImpl.eINSTANCE.createPart();
		saveablePart.setDirty(beforeDirty);
		saveablePart
				.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.application.ClientEditor");
		window.getChildren().add(saveablePart);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		ClientEditor editor = (ClientEditor) saveablePart.getObject();
		editor.setThrowException(throwException);
		window.getContext().set(ISaveHandler.class.getName(),
				new ISaveHandler() {
					public Save[] promptToSave(Collection<MPart> saveablePart) {
						return null;
					}
					public Save promptToSave(MPart saveablePart) {
						return returnValue;
					}
				});
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		if (beforeDirty) {
			assertEquals(success, partService.savePart(saveablePart, confirm));
		} else {
			assertTrue(
					"The part is not dirty, the save operation should complete successfully",
					partService.savePart(saveablePart, confirm));
		}
		assertEquals(afterDirty, saveablePart.isDirty());