Error:

0:05:47 load avg: 5.95 [311/423/2] test_genericalias failed -- running: test_multiprocessing_spawn (1 min 59 sec)
test test_genericalias crashed -- Traceback (most recent call last):                                                                                                                         
  File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 272, in _runtest_inner        
    refleak = _runtest_inner2(ns, test_name)                                                                                                                                                 
  File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 223, in _runtest_inner2         
    the_module = importlib.import_module(abstest)                                                                                                                                            
  File "/home/vstinner/python/master/Lib/importlib/__init__.py", line 126, in import_module                                                                                                  
    return _bootstrap._gcd_import(name[level:], package, level)                                                                                                                              
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import                                                                                                                            
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load                                                                                                                         
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked                                                                                                                 
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked                                                                                                                          
  File "<frozen importlib._bootstrap_external>", line 790, in exec_module                                                                                                                    
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed                                                                                                               
  File "/home/vstinner/python/master/Lib/test/test_genericalias.py", line 16, in <module>                                                                                                    
    from ctypes import Array, LibraryLoader
  File "/home/vstinner/python/master/Lib/ctypes/__init__.py", line 8, in <module>
    from _ctypes import Union, Structure, Array 
ModuleNotFoundError: No module named '_ctypes'


The minimum fix is to skip test_genericalias is ctypes is missing. For example, use "ctypes = support.import_helper.import_module('ctypes')" to import ctypes.

See also bpo-41476: test_zoneinfo fails if the _lzma module is missing.