'Selecting a column that doesn\'t exist fails'

def test_select_columns_fail(self, table_data):

    self.t = table_data.Table(table_data.COLS)
    with pytest.raises(ValueError) as err:
        self.t[['xxxx']]
    assert ('Slice    name(s)    xxxx    not    valid    column    name(s)' in str(err))
    with pytest.raises(ValueError) as err:
        self.t[['xxxx', 'yyyy']]
    assert ('Slice    name(s)    xxxx,    yyyy    not    valid    column    name(s)' in str(err))
