I don't see anything odd -- it runs for awhile and then times out once it's deadlocked:

0:03:18 load avg: 3.20 [224] test_multiprocessing_forkserver             
test_many_processes (test.test_multiprocessing_forkserver.WithProcessesTestProcess) ... ok                                                         
test_many_processes (test.test_multiprocessing_forkserver.WithThreadsTestProcess) ... skipped 'test not appropriate for threads'                   

----------------------------------------------------------------------   
Ran 2 tests in 0.849s               

OK (skipped=1)                      
0:03:18 load avg: 3.11 [225] test_multiprocessing_forkserver             
test_many_processes (test.test_multiprocessing_forkserver.WithProcessesTestProcess) ... ok                                                         
test_many_processes (test.test_multiprocessing_forkserver.WithThreadsTestProcess) ... skipped 'test not appropriate for threads'                   

----------------------------------------------------------------------   
Ran 2 tests in 0.865s               

OK (skipped=1)                      
0:03:19 load avg: 3.11 [226] test_multiprocessing_forkserver             
test_many_processes (test.test_multiprocessing_forkserver.WithProcessesTestProcess) ... Timeout (0:00:30)!                                         
Thread 0x00007fff790c1000 (most recent call first):                      
  File "/Users/mattb/src/misc/cpython/Lib/selectors.py", line 415 in select                                                                        
  File "/Users/mattb/src/misc/cpython/Lib/multiprocessing/connection.py", line 916 in wait                                                         
  File "/Users/mattb/src/misc/cpython/Lib/multiprocessing/popen_fork.py", line 45 in wait                                                          
  File "/Users/mattb/src/misc/cpython/Lib/multiprocessing/process.py", line 121 in join                                                            
  File "/Users/mattb/src/misc/cpython/Lib/test/_test_multiprocessing.py", line 431 in test_many_processes                                          
  File "/Users/mattb/src/misc/cpython/Lib/unittest/case.py", line 605 in run                                                                       
  File "/Users/mattb/src/misc/cpython/Lib/unittest/case.py", line 653 in __call__                                                                  
  File "/Users/mattb/src/misc/cpython/Lib/unittest/suite.py", line 122 in run                                                                      
  File "/Users/mattb/src/misc/cpython/Lib/unittest/suite.py", line 84 in __call__                                                                  
  File "/Users/mattb/src/misc/cpython/Lib/unittest/suite.py", line 122 in run                                                                      
  File "/Users/mattb/src/misc/cpython/Lib/unittest/suite.py", line 84 in __call__                                                                  
  File "/Users/mattb/src/misc/cpython/Lib/unittest/suite.py", line 122 in run                                                                      
  File "/Users/mattb/src/misc/cpython/Lib/unittest/suite.py", line 84 in __call__                                                                  
  File "/Users/mattb/src/misc/cpython/Lib/unittest/runner.py", line 176 in run                                                                     
  File "/Users/mattb/src/misc/cpython/Lib/test/support/__init__.py", line 1896 in _run_suite                                                       
  File "/Users/mattb/src/misc/cpython/Lib/test/support/__init__.py", line 1936 in run_unittest                                                     
  File "/Users/mattb/src/misc/cpython/Lib/test/libregrtest/runtest.py", line 168 in test_runner                                                    
  File "/Users/mattb/src/misc/cpython/Lib/test/libregrtest/runtest.py", line 169 in runtest_inner                                                  
  File "/Users/mattb/src/misc/cpython/Lib/test/libregrtest/runtest.py", line 137 in runtest                                                        
  File "/Users/mattb/src/misc/cpython/Lib/test/libregrtest/main.py", line 374 in run_tests_sequential                                              
  File "/Users/mattb/src/misc/cpython/Lib/test/libregrtest/main.py", line 454 in run_tests                                                         
  File "/Users/mattb/src/misc/cpython/Lib/test/libregrtest/main.py", line 530 in _main                                                             
  File "/Users/mattb/src/misc/cpython/Lib/test/libregrtest/main.py", line 504 in main                                                              
  File "/Users/mattb/src/misc/cpython/Lib/test/libregrtest/main.py", line 573 in main                                                              
  File "/Users/mattb/src/misc/cpython/Lib/test/__main__.py", line 2 in <module>                                                                    
  File "/Users/mattb/src/misc/cpython/Lib/runpy.py", line 85 in _run_code                                                                          
  File "/Users/mattb/src/misc/cpython/Lib/runpy.py", line 193 in _run_module_as_main