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
stackC.setSelectedElement(partC);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = window.getContext().get(EPartService.class);
		partService.activate(partA);
		partService.hidePart(partA);
		MPart activePart = partService.getActivePart();
		if (activePart == partB) {
			partService.hidePart(partB);
			assertEquals(partC, partService.getActivePart());
		} else if (activePart == partC) {
			partService.hidePart(partC);
			assertEquals(partB, partService.getActivePart());
		} else if (activePart == partA) {
			fail("Part A should have been deactivated");
		} else {
			fail("Another part should have been activated");
		}
	}
	public void testHidePart_ActivationHistory11() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		window.getSharedElements().add(partA);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		window.getSharedElements().add(partB);
		MPart partC = BasicFactoryImpl.eINSTANCE.createPart();