The test_help_with_metavar test appears to be broken.

It fails with an assertion error:
AssertionError: 'usag[55 chars]_name [-h] [--proxy <http[s]://example:1234>]\[113 chars]4>\n' != 'usag[55 chars]_name\n       [-h] [--proxy <http[s]://example[121 chars]4>\n'

If I change 
"this_is_spammy_prog_with_a_long_name_sorry_about_the_name
                   [-h] [--proxy <http[s]://example:1234>]"

to

"this_is_spammy_prog_with_a_long_name_sorry_about_the_name [-h] [--proxy <http[s]://example:1234>]"

i.e. move the part starting with '[-h]' onto the same line, the test passes. 

What is the correct output expected here? I would think the [-h] should be on the same line, but maybe this is intended behavior and the problem is with my system. No other unit test is failing for me though.

Tests were added with 842985f6c70484ed7b8fc30d0bc05aec73236a98 and passes on master and 3.7.1 . Can you please add the full traceback and the command you used to run the test? Also the output of python version as below to try reproducing it  

python -m test.pythoninfo | grep 'sys.version:'

Output from running "python3 -m test.pythoninfo | grep 'sys.version:'":
sys.version: 3.7.2 (default, Feb 17 2019, 11:51:43)  [GCC 4.8.5 20150623 (Red Hat 4.8.5-28)]

Btw, I am running 3.7.2 because that's the latest version offered on https://www.python.org/downloads/

Ah sorry, forgot the traceback and command:

Command: python3 Lib/test/test_argparse.py 
test (__main__.TestActionRegistration) ... ok
test_failures_many_groups_listargs (__main__.TestActionUserDefined) ... ok
test_failures_many_groups_sysargs (__main__.TestActionUserDefined) ... ok
...
...
======================================================================
FAIL: test_help_with_metavar (__main__.TestWrappingMetavar)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "Lib/test/test_argparse.py", line 5152, in test_help_with_metavar
    '''))
AssertionError: 'usag[55 chars]_name [-h] [--proxy <http[s]://example:1234>]\[113 chars]4>\n' != 'usag[55 chars]_name\n       [-h] [--proxy <http[s]://example[121 chars]4>\n'
- usage: this_is_spammy_prog_with_a_long_name_sorry_about_the_name [-h] [--proxy <http[s]://example:1234>]
?                                                                 ----------------------------------------
+ usage: this_is_spammy_prog_with_a_long_name_sorry_about_the_name
+        [-h] [--proxy <http[s]://example:1234>]
  
  optional arguments:
    -h, --help            show this help message and exit
    --proxy <http[s]://example:1234>


----------------------------------------------------------------------

Ran 1574 tests in 4.558s

FAILED (failures=1)
Traceback (most recent call last):
  File "Lib/test/test_argparse.py", line 5164, in <module>
    test_main()
  File "Lib/test/test_argparse.py", line 5156, in test_main
    support.run_unittest(__name__)
  File "/usr/local/lib/python3.7/test/support/__init__.py", line 1991, in run_unittest
    _run_suite(suite)
  File "/usr/local/lib/python3.7/test/support/__init__.py", line 1910, in _run_suite
    raise TestFailed(err)
test.support.TestFailed: Traceback (most recent call last):
  File "Lib/test/test_argparse.py", line 5152, in test_help_with_metavar
    '''))
AssertionError: 'usag[55 chars]_name [-h] [--proxy <http[s]://example:1234>]\[113 chars]4>\n' != 'usag[55 chars]_name\n       [-h] [--proxy <http[s]://example[121 chars]4>\n'
- usage: this_is_spammy_prog_with_a_long_name_sorry_about_the_name [-h] [--proxy <http[s]://example:1234>]
?                                                                 ----------------------------------------
+ usage: this_is_spammy_prog_with_a_long_name_sorry_about_the_name
+        [-h] [--proxy <http[s]://example:1234>]
  
  optional arguments:
    -h, --help            show this help message and exit
    --proxy <http[s]://example:1234>



I first encountered this error when running "make test" when installing python 3.7.2, then tried running this test manually with the command above.

Thanks for the details. I couldn't reproduce this on a clean v3.7.2 build on Mac. There were also no changes to argparse.py between 3.7.0 and 3.7.2 so I don't know why it's failing on your environment.

➜  cpython git:(9a3ffc0492) git log v3.7.0..v3.7.2 Lib/argparse.py | cat
➜  cpython git:(9a3ffc0492) ./python.exe -m test.pythoninfo | grep 'sys.version:'
sys.version: 3.7.2 (tags/v3.7.2:9a3ffc0492, Feb 17 2019, 10:47:33)  [Clang 7.0.2 (clang-700.1.81)]
➜  cpython git:(9a3ffc0492) ./python.exe -m unittest -v test.test_argparse.TestWrappingMetavar.test_help_with_metavar
test_help_with_metavar (test.test_argparse.TestWrappingMetavar) ... ok

----------------------------------------------------------------------
Ran 1 test in 0.004s

OK

Figured it out. My shell had the COLUMNS environment variable set, and python was inheriting it in os.environ. The failing test case assumes an 80-column screen.

Anyway, looks like it has been fixed for 3.8 here:
https://github.com/python/cpython/commit/74102c9a5f2327c4fc47feefa072854a53551d1f#diff-837b312b1f3508216ace6adb46492836

Closing this item.