## while building python3.7 from source code on debian9.8 stretch.
hardware : intel corei5 3337U
4 Gib -- physical ram//4 Gib -- swap space

following the instructions given in the README.rst file:
user@host $ ./configure --enable-optimizations
#---works fine : no issues

user@host $ make 
#---works fine : noissues

user@host $ make test
produces this 
FAIL: test_locale_flag (test.test_re.ReTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/apoos-maximus/packages/Python-3.7.2/Lib/test/test_re.py", line 1540, in test_locale_flag
    self.assertTrue(pat.match(bletter))
AssertionError: None is not true

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

Ran 123 tests in 1.048s

FAILED (failures=1, skipped=2)
test test_re failed
1 test failed again:
    test_re

== Tests result: FAILURE then FAILURE ==

384 tests OK.

1 test failed:
    test_re

29 tests skipped:
    test_bz2 test_ctypes test_curses test_dbm_gnu test_dbm_ndbm
    test_devpoll test_gdb test_gzip test_idle test_kqueue test_lzma
    test_msilib test_ossaudiodev test_readline test_smtpnet
    test_sqlite test_ssl test_startfile test_tcl test_tix test_tk
    test_ttk_guionly test_ttk_textonly test_turtle test_winconsoleio
    test_winreg test_winsound test_zipfile64 test_zlib

1 re-run test:
    test_re

2 tests run no tests:
    test_dtrace test_future4

Total duration: 4 min 44 sec
Tests result: FAILURE then FAILURE
Makefile:1074: recipe for target 'test' failed
make: *** [test] Error 2


#on rerunning the same test 
user@host $  make test TESTOPTS="-v test_re"

FAIL: test_locale_flag (test.test_re.ReTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/apoos-maximus/packages/Python-3.7.2/Lib/test/test_re.py", line 1540, in test_locale_flag
    self.assertTrue(pat.match(bletter))
AssertionError: None is not true

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

Ran 123 tests in 0.750s

FAILED (failures=1, skipped=2)
test test_re failed
1 test failed again:
    test_re

== Tests result: FAILURE then FAILURE ==

1 test failed:
    test_re

1 re-run test:
    test_re

Total duration: 1 sec 646 ms
Tests result: FAILURE then FAILURE
Makefile:1074: recipe for target 'test' failed
make: *** [test] Error 2




###### this is how the bug could be reproduced 
PS: do have a look at the traceback ::it makes no sense to me, it might to you !