Bug 327964 EPartService's hidePart may fail when trying to hide a shared part that's in a shared container
The placeholder retrieval code in the EPartService implementation doesn't go far down deep enough and actually stops at the shared container level. This causes the placeholder of the shared part to not be found.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
testIsPartVisible_NotInStack(true, false);
	}
	public void testIsPartVisible_NotInStackFalseTrue() {
		testIsPartVisible_NotInStack(false, true);
	}
	public void testIsPartVisible_NotInStackFalseFalse() {
		testIsPartVisible_NotInStack(false, false);
	}
	public void testIsPartVisible_ViewVisible() {
		MApplication application = createApplication("partId");
		MWindow window = application.getChildren().get(0);
		MPartStack partStack = (MPartStack) window.getChildren().get(0);
		MPart part = (MPart) partStack.getChildren().get(0);
		partStack.setSelectedElement(part);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		assertTrue(partService.isPartVisible(part));
	}
	public void testIsPartVisible_ViewVisible_myService() {
		MApplication application = createApplication("partId");
		MWindow window = application.getChildren().get(0);
		MPartStack partStack = (MPartStack) window.getChildren().get(0);
		MPart part = (MPart) partStack.getChildren().get(0);
		partStack.setSelectedElement(part);
		getEngine().createGui(window);
		EPartService partService = (EPartService) part.getContext().get(
				EPartService.class.getName());
		assertTrue(partService.isPartVisible(part));
	}