Currently, test_etree has a Python 2 shim importing cElementTree and skipping the test on ImportError. Since cElementTree was deprecated and removed in Python 3 with 36543. So this test is now skipped. The fix would be to remove the shim and import Element from xml.etree.ElementTree. This is a good beginner issue. Test log as below : 

./python -m test test_typing -m test_etree -vvv
== CPython 3.9.0a5+ (heads/master:33f15a16d4, Mar 27 2020, 11:15:48) [GCC 7.5.0]
== Linux-4.15.0-66-generic-x86_64-with-glibc2.27 little-endian
== cwd: /root/cpython/build/test_python_24162
== CPU count: 1
== encodings: locale=UTF-8, FS=utf-8
0:00:00 load avg: 0.07 Run tests sequentially
0:00:00 load avg: 0.07 [1/1] test_typing
test_etree (test.test_typing.UnionTests) ... skipped 'cElementTree not found'

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

Ran 1 test in 0.001s

OK (skipped=1)

== Tests result: SUCCESS ==

1 test OK.

Total duration: 150 ms
Tests result: SUCCESS