Bug 329184 Detached view that is an activation target candidate can prevent perspective switching
1. Detach the 'Outline' view. 2. Window > Open Perspective > Debug 3. Window > Open Perspective > Java 4. The perspective switch doesn't actually happen. You see the 'Debug' perspective's content with an 'Outline' view detached. Closing the 'Outline' view in the 'Debug' perspective will workaround this problem.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		partService.activate(partA);
		assertEquals(partA, partService.getActivePart());
		MPart shownPart = partService.showPart("partB",
				EPartService.PartState.VISIBLE);
		assertEquals(2, partStack.getChildren().size());
		assertEquals(
				"The part is in the same stack as the active part, so the active part should not have changed",
				partA, partService.getActivePart());
		assertNotNull("The shown part should have a context",
				partB.getContext());
		assertTrue(partService.isPartVisible(partA));
		assertFalse(partService.isPartVisible(partB));
		assertEquals(partB, shownPart);
		assertTrue(partB.isToBeRendered());
	}
	private void testShowPart_Id_Unrendered(EPartService.PartState partState) {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPart part = BasicFactoryImpl.eINSTANCE.createPart();
		part.setElementId("partId");
		part.setToBeRendered(false);
		window.getChildren().add(part);
		initialize(applicationContext, application);