[MRG] Replace stdout / stderr switching in smoke tests with capsys.

[kdexd]

Fixes #457

Since joblib now uses pytest instead of nose, one does not need to explicitly capture the output. In many tests, sys.stdout and sys.stderr were temporarily replaced by a dummy StringIO or tempfile, which were restored back after test execution completed.

This manual switching is now removed owing to default behaviour of pytest (refer #457 description). Pytest's capsys fixture is used to grab the output and perform regex matching.

[kdexd]

kd@dragonstone:~/Documents/joblib$ git grep sys.stdout joblib/test/test*.py
joblib/test/test_memory.py:    sys.stdout.write('Reloading\n')
joblib/test/test_testing.py:        'sys.stdout.flush()',
joblib/test/test_testing.py:        'sys.stdout.flush()'])
kd@dragonstone:~/Documents/joblib$ git grep sys.stderr joblib/test/test*.py
joblib/test/test_testing.py:        'sys.stderr.write("writing on stderr")',
joblib/test/test_testing.py:        'sys.stderr.write("before sleep on stderr")',
joblib/test/test_testing.py:        'sys.stderr.flush()',

Only these occurences remain in test files.

[kdexd]

@lesteve Is it appropriate to use print here ?

[lesteve]

sys.stdout.write is fine.

[lesteve]

Hmmm interesting, so the captured stdout was not used at all, right? I am wondering why it was done like this.

I am wondering whether it would be worth doing some testing of the Parallel logging. Maybe not in this test though.

[kdexd]

@lesteve I am getting lines like:

[Parallel(n_jobs=?)]: Done   ? out of   ? | elapsed:    ?.?s remaining:    ?.?s

where ? is a digit.

[lesteve]

I was saying this more for another PR and this is not super high priority, but you could add a test function that would check (bunch of random ideas, not all of them are worth pursuing):

• verbose=0 does not print anything
• n_jobs is set correctly in the printout
• done is > 0 and growing
• elapsed is growing
• remaining is never negative (we had a bug like this at some point) and maybe decreasing (not sure about that it could well be some oscillations)
• with increasing verbose you get more and more lines in your output

Not super high priority but nice to have and fun to write ;-).

[kdexd]

Noted for a future PR. 😉

[kdexd]

@lesteve Anything more to be added here ? I took up this work first because the huge chunk in test_memory.py was distracting a bit.. Once this is merged, I'll be able to quickly open a PR for removing yield based tests from test_memory.py, continuing on #411..

[lesteve]

LGTM, merging thanks!