### Question:
PreviewDiagramScreen { @OnOpen @SuppressWarnings("unused") public void onOpen() { final ClientSession current = clientSessionManager.getCurrentSession(); if (Objects.nonNull(current)) { showPreview(current); } } protected  PreviewDiagramScreen(); @Inject  PreviewDiagramScreen(final SessionManager clientSessionManager,
                                final @Any @DMNEditor ManagedInstance<SessionDiagramPreview<AbstractSession>> sessionPreviews,
                                final View view,
                                final DMNDiagramsSession session); @OnStartup @SuppressWarnings("unused") void onStartup(final PlaceRequest placeRequest); @OnOpen @SuppressWarnings("unused") void onOpen(); @OnClose @SuppressWarnings("unused") void onClose(); @WorkbenchPartTitle @SuppressWarnings("unused") String getTitle(); @WorkbenchPartView @SuppressWarnings("unused") IsWidget getWidget(); @WorkbenchContextId @SuppressWarnings("unused") String getMyContextRef(); static final String SCREEN_ID; }### Answer:
@Test public void testOnOpen() { tested.onOpen(); verify(tested).showPreview(any()); }