'Access TableColumns by position and show that item access returns
a Column that refers to underlying table data'

def test_by_position(self, table_data):

    self.t = table_data.Table(table_data.COLS)
    self.tc = self.t.columns
    assert (self.tc[1].name == 'b')
    assert np.all((self.tc[1].data == table_data.COLS[1].data))
    assert (self.tc[1].description == 'db')
    assert (self.tc[1].format == 'fb')
    assert (self.tc[1].meta == {'mb': 1})
    assert (self.tc[1].unit == 'ub')
    assert self.tc[1].attrs_equal(table_data.COLS[1])
    assert isinstance(self.tc[1], table_data.Column)
    assert (self.tc[2].unit == 'ub')
    self.tc[1][1] = 0
    assert (self.t['b'][1] == 0)
