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One test of test_os fails on an android emulator running an x86 system image at API level 21.
See the attached test_output.txt file.

On android dup2() returns with an error when both fds are the same:
root@generic_x86:/data/local/tmp # python
Python 3.6.0a0 (default:811ccdee6f87+, May 7 2016, 12:44:06) 
[GCC 4.9 20140827 (prerelease)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.dup2(1, 1)
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
OSError: [Errno 22] Invalid argument
The attached patch fixes this in test_urandom_fd_reopened.

I think this is an Android bug. See specification <http://pubs.opengroup.org/onlinepubs/9699919799/functions/dup2.html>, fix <https://android.googlesource.com/platform/bionic/+/be52e658171edf6651895c40d1563289bafa52f7%5E!/>.
If the change is to go into Python, it would be good to include a comment admitting it is an Android workaround, rather than a general deficiency.

Since this seems to be fixed in a version of android that is more recent that API 21, maybe use the value of 'sdk.release' when platform.android_ver() is available after issue #26855 is fixed, with for example, if this is fixed at API 23:
 sdk_release = platform.android_ver()[1]
 if new_fd != fd or not sdk_release or sdk_release >= 23:

Yes something like that should do the trick

My implementation at #26855 returns a tuple of strings like other funcitons, including java_ver() and mac_ver(). Maybe it requires a change.

This is fixed at API 23 (Android 6.0) and test_os runs on an android-23-x86 emulator without failures.

This new patch takes into account Martin comment in msg265099 and fixes a call to getpwall() as Android does not have getpwall().

New patch. Thanks for the review Martin!

New changeset 80e4cb5888f3 by Xavier de Gaye in branch '3.6':
Issue #26935: Fix broken Android dup2() in test_os
https://hg.python.org/cpython/rev/80e4cb5888f3
New changeset da59b7084dbe by Xavier de Gaye in branch 'default':
Issue #26935: Merge 3.6
https://hg.python.org/cpython/rev/da59b7084dbe