Bug 303218 Active part no longer seems to be queryable from the application's context
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
MApplication application = createApplication("partId", "partId2");
		MWindow window = application.getChildren().get(0);
		MPartStack partStack = (MPartStack) window.getChildren().get(0);
		partStack.setSelectedElement(partStack.getChildren().get(0));
		getEngine().createGui(window);
		MPart part = partStack.getChildren().get(1);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		assertFalse(partService.isPartVisible(part));
	}
	public void testIsPartVisible_ViewNotVisible_myService() {
		MApplication application = createApplication("partId", "partId2");
		MWindow window = application.getChildren().get(0);
		MPartStack partStack = (MPartStack) window.getChildren().get(0);
		partStack.setSelectedElement(partStack.getChildren().get(0));
		getEngine().createGui(window);
		MPart part1 = partStack.getChildren().get(0);
		MPart part2 = partStack.getChildren().get(1);
		EPartService partService1 = (EPartService) part1.getContext().get(
				EPartService.class.getName());
		assertTrue(partService1.isPartVisible(part1));
		assertFalse(partService1.isPartVisible(part2));
		partService1.activate(part2);
		EPartService partService2 = (EPartService) part2.getContext().get(
				EPartService.class.getName());
		assertFalse(partService1.isPartVisible(part1));
		assertTrue(partService1.isPartVisible(part2));
		assertFalse(partService2.isPartVisible(part1));
		assertTrue(partService2.isPartVisible(part2));
	}