@Test
public void testDeleteAllColumns() {

    final String sql = "delete from Column c";
    final Query query = mock(Query.class);
    when(persistenceManager.createQuery(sql)).thenReturn(query);
    columnStorage.deleteAll();
    verify(persistenceManager, times(1)).createQuery(sql);
    verifyNoMoreInteractions(persistenceManager);
    verify(query, times(1)).executeUpdate();
    verifyNoMoreInteractions(query);
}