tests/test-dirs.py

histedit: remove an unnecessary default value of `b''` for commit message

I don't think `ctx.description()` is ever anything falsy other than
`b''`. I think the comment added in 4c4232e51167 (histedit: extract
common summary code into method, 2016-05-27) is mistaken (I don't see
any code following that pattern before the function was added).

Differential Revision: https://phab.mercurial-scm.org/D12406

import unittest

import silenttestrunner

from mercurial import pathutil


class dirstests(unittest.TestCase):
    def testdirs(self):
        for case, want in [
            (b'a/a/a', [b'a', b'a/a', b'']),
            (b'alpha/beta/gamma', [b'', b'alpha', b'alpha/beta']),
        ]:
            d = pathutil.dirs([])
            d.addpath(case)
            self.assertEqual(sorted(d), sorted(want))

    def testinvalid(self):
        with self.assertRaises(ValueError):
            d = pathutil.dirs([])
            d.addpath(b'a//b')


if __name__ == '__main__':
    silenttestrunner.main(__name__)