human
I wrote the below code

    def all_positive(column):
        if np.any((column < 0)):
            return False
        return True
    t = Table.read(['    a    c    d', '    -2    7.0    0', '    -2    5.0    1', '    0    0.0    4', '    1    3.0    5', '    1    2.0    -6', '    1    1.0    7', '    3    3.0    5', '    3    -2.0    6', '    3    1.0    7'], format='ascii')
    tg = t.group_by('a')
    c2 = tg['c'].groups.filter(all_positive)
    assert (len(c2.groups) == 3)
    assert (c2.groups[0].pformat() == ['    c    ', '---', '7.0', '5.0'])
    assert (c2.groups[1].pformat() == ['    c    ', '---', '0.0'])
    assert (c2.groups[2].pformat() == ['    c    ', '---', '3.0', '2.0', '1.0'])

What's a good function header?
 ... Here's a good function header?
assistant
#Here's a good function header.

def test_column_filter():