vstinner@apu$ ./python -Werror -m test -v test_platform

======================================================================
ERROR: test_dist (test.test_platform.PlatformTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/vstinner/prog/python/3.7/Lib/test/test_platform.py", line 270, in test_dist
    res = platform.dist()
  File "/home/vstinner/prog/python/3.7/Lib/platform.py", line 379, in dist
    "in Python 3.5", DeprecationWarning, stacklevel=2)
DeprecationWarning: dist() and linux_distribution() functions are deprecated in Python 3.5

======================================================================
ERROR: test_linux_distribution_encoding (test.test_platform.PlatformTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/vstinner/prog/python/3.7/Lib/test/test_platform.py", line 346, in test_linux_distribution_encoding
    distname, version, distid = platform.linux_distribution()
  File "/home/vstinner/prog/python/3.7/Lib/platform.py", line 305, in linux_distribution
    "in Python 3.5", DeprecationWarning, stacklevel=2)
DeprecationWarning: dist() and linux_distribution() functions are deprecated in Python 3.5

The code calling the deprecated function should be surrounded by something like that:

with support.check_warnings(('cgi.parse_qs is deprecated', DeprecationWarning)):

Python 3.8 (master branch), platform.linux_distribution() and its the tests have been removed: see bpo-28167.

I was looking into this and it seems that using replacing PendingDeprecationWarning with DeprecationWarning fixes the issue. Should I be using check_warnings?

Attaching a patch of this so that I can raise a PR for the same.

I grepped for PendingDeprecationWarning and there is a similar crash with test_ssl

➜  cpython git:(1bf9cc5) ✗ ./python -Werror -m test -v test_ssl
== CPython 3.7.0 (v3.7.0:1bf9cc5, Jun 28 2018, 11:20:40) [GCC 5.4.0 20160609]
== Linux-4.4.0-127-generic-x86_64-with-debian-stretch-sid little-endian
== cwd: /home/cpython/build/test_python_31365
== CPU count: 1
== encodings: locale=UTF-8, FS=utf-8
Run tests sequentially
0:00:00 load avg: 0.08 [1/1] test_ssl
test test_ssl crashed -- Traceback (most recent call last):
  File "/home/cpython/Lib/test/libregrtest/runtest.py", line 176, in runtest_inner
    test_runner()
  File "/home/cpython/Lib/test/test_ssl.py", line 4151, in test_main
    plat = func()
  File "/home/cpython/Lib/platform.py", line 305, in linux_distribution
    "in Python 3.5", DeprecationWarning, stacklevel=2)
DeprecationWarning: dist() and linux_distribution() functions are deprecated in Python 3.5

test_ssl failed

== Tests result: FAILURE ==

1 test failed:
    test_ssl

Total duration: 194 ms
Tests result: FAILURE

Thanks

Would you mind to create a PR instead of a patch file?

New changeset f5770f354cb982303237d581ad2b296486475965 by Victor Stinner (Xtreak) in branch '3.7':
bpo-33988: Fix test_warnings using -W error (GH-7985)
https://github.com/python/cpython/commit/f5770f354cb982303237d581ad2b296486475965

Thank you Karthikeyan Singaravelan for your fix!