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test_pipes fails on an android emulator running an x86 system image at API level 21.
root@generic_x86:/data/local/tmp # python -m test -v test_pipes
== CPython 3.6.0a0 (default:f4c6dab59cd8+, May 3 2016, 10:42:45) [GCC 4.9 20140827 (prerelease)]
== Linux-3.4.67+-i686-with-libc little-endian
== hash algorithm: fnv 32bit
== /data/local/tmp/test_python_1927
Testing with flags: sys.flags(debug=0, inspect=0, interactive=0, optimize=0, dont_write_bytecode=0, 
no_user_site=0, no_site=0, ignore_environment=0, verbose=0, bytes_warning=0, quiet=0, hash_randomiza
tion=1, isolated=0)
Run tests sequentially
0:00:00 [1/1] test_pipes
testBadAppendOptions (test.test_pipes.SimplePipeTests) ... ok
testBadOpenMode (test.test_pipes.SimplePipeTests) ... ok
testBadPrependOptions (test.test_pipes.SimplePipeTests) ... ok
testClone (test.test_pipes.SimplePipeTests) ... ok
testEmptyPipeline1 (test.test_pipes.SimplePipeTests) ... ok
testEmptyPipeline2 (test.test_pipes.SimplePipeTests) ... ok
testEmptyPipeline3 (test.test_pipes.SimplePipeTests) ... ok
testReadOpenSink (test.test_pipes.SimplePipeTests) ... ok
testRepr (test.test_pipes.SimplePipeTests) ... ok
testSetDebug (test.test_pipes.SimplePipeTests) ... ok
testSimplePipe1 (test.test_pipes.SimplePipeTests) ... /system/bin/sh: tr: not found
FAIL
testSimplePipe2 (test.test_pipes.SimplePipeTests) ... sh: tr: not found
FAIL
testSimplePipe3 (test.test_pipes.SimplePipeTests) ... /system/bin/sh: tr: not found
FAIL
testWriteOpenSource (test.test_pipes.SimplePipeTests) ... ok
======================================================================
FAIL: testSimplePipe1 (test.test_pipes.SimplePipeTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/sdcard/org.bitbucket.pyona/lib/python3.6/test/test_pipes.py", line 27, in testSimplePipe1
 self.assertEqual(f.read(), 'HELLO WORLD #1')
AssertionError: '' != 'HELLO WORLD #1'
+ HELLO WORLD #1
======================================================================
FAIL: testSimplePipe2 (test.test_pipes.SimplePipeTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/sdcard/org.bitbucket.pyona/lib/python3.6/test/test_pipes.py", line 36, in testSimplePipe2
 self.assertEqual(f.read(), 'HELLO WORLD #2')
AssertionError: '' != 'HELLO WORLD #2'
+ HELLO WORLD #2
======================================================================
FAIL: testSimplePipe3 (test.test_pipes.SimplePipeTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/sdcard/org.bitbucket.pyona/lib/python3.6/test/test_pipes.py", line 45, in testSimplePipe3
 self.assertEqual(f.read(), 'HELLO WORLD #2')
AssertionError: '' != 'HELLO WORLD #2'
+ HELLO WORLD #2
----------------------------------------------------------------------
Ran 14 tests in 0.039s
FAILED (failures=3)
test test_pipes failed
1 test failed:
 test_pipes
Total duration: 0:00:01

The attached patch fixes this.

Is tr not available on Android?! I would suggest to use sed instead, but I afraid sed is not available too. What commands are available at all?

Here is the list of commands at /system/bin on the emulator.

Thanks for the review Serhiy. New patch attached.

New changeset 3bad4b0f7612 by Serhiy Storchaka in branch 'default':
Issue #26918: Skipped some tests in test_pipes on Android.
https://hg.python.org/cpython/rev/3bad4b0f7612 

LGTM. Thanks Xavier.
It looks to me that there are no useful commands that can be used for testing on Android. We could use md5 or grep, but this would require rewriting tests too much for small benefit. It is better to skip tests.

Ooops too late. Here is a new patch that replaces the tr command and allows all the tests of test_pipes to run successfully on android.

The equivalent of used "tr" command is .upper(), not .swapcase().
Instead of the loop
 for s in sys.stdin.read(): sys.stdout.write(s.upper())
you can write just
 sys.stdout.write(sys.stdin.read().upper())
But actually the loop is needed for testing purpose.
 while True:
 b = sys.stdin.buffer.read(1)
 if not b:
 break
 sys.stdout.buffer.write(b.upper())
And sys.executable should be escaped for the case of spaces or other special symbols in the path.
All this complicates tests too much. I prefer to skip some tests on Android.

I agree with not complicating tests too much.
For the record, the pipes test suite coverage is very low and the code paths that lead to invocations of os.popen() in the pipes module are not tested when those three tests are skipped.