'Test whether locator marks subs to be labeled'

def _sub_labels(self, axis, subs=()):

    fmt = axis.get_minor_formatter()
    minor_tlocs = axis.get_minorticklocs()
    fmt.set_locs(minor_tlocs)
    coefs = (minor_tlocs / (10 ** np.floor(np.log10(minor_tlocs))))
    label_expected = [(np.round(c) in subs) for c in coefs]
    label_test = [(fmt(x) != u'') for x in minor_tlocs]
    assert (label_test == label_expected)
