Bug 321757 EPS adds a part without considering its placeholder if target container is not a part stack
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
applicationContext);
			assertTrue(newEngine instanceof IPresentationEngine);
			applicationContext.set(IPresentationEngine.class.getName(),
					newEngine);
			engine = (IPresentationEngine) newEngine;
		}
		return engine;
	}
	public void testFindPart_PartInWindow() {
		MApplication application = createApplication("partId");
		MWindow window = application.getChildren().get(0);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		MPart part = partService.findPart("partId");
		assertNotNull(part);
		MPartStack partStack = (MPartStack) window.getChildren().get(0);
		assertEquals(partStack.getChildren().get(0), part);
		part = partService.findPart("invalidPartId");
		assertNull(part);
	}
	public void testFindPart_PartNotInWindow() {
		MApplication application = createApplication("partId");
		MWindow window = application.getChildren().get(0);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		MPart part = partService.findPart("invalidPartId");
		assertNull(part);
	}