ImportError is raised only when python -m unittest discover is given

[Hirokih2Horiuchi]

BPO	31840
Nosy	@pfmoore, @ronaldoussoren, @tjguk, @ned-deily, @zware, @serhiy-storchaka, @zooba
Files	test.py: runs or raises

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2017-10-22.06:30:25.502>
created_at = <Date 2017-10-22.06:06:57.230>
labels = ['OS-mac', 'type-bug', 'library', 'invalid', 'tests', 'OS-windows']
title = '`ImportError` is` raised` only when `python -m unittest discover` is given'
updated_at = <Date 2017-10-22.06:30:25.489>
user = 'https://bugs.python.org/Hirokih2Horiuchi'

bugs.python.org fields:

activity = <Date 2017-10-22.06:30:25.489>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2017-10-22.06:30:25.502>
closer = 'serhiy.storchaka'
components = ['Library (Lib)', 'macOS', 'Tests', 'Windows']
creation = <Date 2017-10-22.06:06:57.230>
creator = 'Hiroki \xe2\x80\x9ch2\xe2\x80\x9d Horiuchi'
dependencies = []
files = ['47230']
hgrepos = []
issue_num = 31840
keywords = []
message_count = 2.0
messages = ['304729', '304731']
nosy_count = 8.0
nosy_names = ['paul.moore', 'ronaldoussoren', 'tim.golden', 'ned.deily', 'zach.ware', 'serhiy.storchaka', 'steve.dower', 'Hiroki \xe2\x80\x9ch2\xe2\x80\x9d Horiuchi']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31840'
versions = ['Python 2.7', 'Python 3.6']

[Hirokih2Horiuchi]

Create a package pkg. Put test.py there. Write none = None in pkg/__init__.py.
In the directory containing pkg/, python [23] -m unittest pkg.test will terminate normally, but python [23] -m unittest discover pkg will raise ImportError. The phenomenon is the same in macOS Sierra, Debian 9.0, Windows 7. I do not think this is a very kind behavior.
Thank you.

[serhiy-storchaka]

Run

python -m unittest discover --start-directory pkg --top-level-directory .

By default the top level directory is the same as the start directory (i.e. pkg).