I'm able to reproduce the bug on Linux as well. I able to reproduce the bug on 3.7 and master, but the bug seems random. Example on Linux with master:

vstinner@apu$ ./python -X utf8 -m test test_pkg 
Run tests sequentially
0:00:00 load avg: 1.30 [1/1] test_pkg

== Tests result: SUCCESS ==

1 test OK.

Total duration: 73 ms
Tests result: SUCCESS
vstinner@apu$ ./python -X utf8 -m test test_pkg 
Run tests sequentially
0:00:00 load avg: 1.35 [1/1] test_pkg

== Tests result: SUCCESS ==

1 test OK.

Total duration: 72 ms
Tests result: SUCCESS
vstinner@apu$ ./python -X utf8 -m test test_pkg 
Run tests sequentially
0:00:00 load avg: 1.35 [1/1] test_pkg
test test_pkg failed -- Traceback (most recent call last):
  File "/home/vstinner/prog/python/master/Lib/test/test_pkg.py", line 260, in test_7
    '__name__', '__package__', '__path__', '__spec__'])
AssertionError: Lists differ: ['__c[34 chars]__loader__', '__name__', '__package__', '__spec__'] != ['__c[34 chars]__loader__', '__name__', '__package__', '__path__', '__spec__']

First differing element 6:
'__spec__'
'__path__'

Second list contains 1 additional elements.
First extra element 7:
'__spec__'

  ['__cached__',
   '__doc__',
   '__file__',
   '__loader__',
   '__name__',
   '__package__',
+  '__path__',
   '__spec__']

test_pkg failed

== Tests result: FAILURE ==

1 test failed:
    test_pkg

Total duration: 74 ms
Tests result: FAILURE