testing with sox only when sox is available

[vincentqb]

Address RuntimeError in Windows CI tests that occur due to sox not being present, see here.

@peterjc123 -- please let me know if this indeed reduces the number of errors in windows.

[peterjc123]

Sorry for late reply. The test result is listed as follows:

(base) audio\test>pytest . --maxfail 10000000000
================================================= test session starts =================================================
platform win32 -- Python 3.7.4, pytest-5.2.1, py-1.8.0, pluggy-0.13.0
plugins: arraydiff-0.3, doctestplus-0.4.0, openfiles-0.4.0, remotedata-0.3.2
collected 75 items / 1 errors / 74 selected

======================================================= ERRORS ========================================================
______________________________________ ERROR collecting test/test_functional.py _______________________________________
test_functional.py:35: in <module>
    class TestFunctional(unittest.TestCase):
test_functional.py:44: in TestFunctional
    waveform_train, sr_train = torchaudio.load(test_filepath)
..\torchaudio\__init__.py:86: in load
    filetype=filetype,
..\torchaudio\_soundfile_backend.py:86: in load
    filepath, frames=num_frames, start=offset, dtype="float32", always_2d=True
\Anaconda3\lib\site-packages\soundfile.py:257: in read
    subtype, endian, format, closefd) as f:
\Anaconda3\lib\site-packages\soundfile.py:629: in __init__
    self._file = self._open(file, mode_int, closefd)
\Anaconda3\lib\site-packages\soundfile.py:1184: in _open
    "Error opening {0!r}: ".format(self.name))
\Anaconda3\lib\site-packages\soundfile.py:1357: in _error_check
    raise RuntimeError(prefix + _ffi.string(err_str).decode('utf-8', 'replace'))
E   RuntimeError: Error opening '\\AppData\\Local\\Temp\\tmp1nhtbbu0\\assets\\steam-train-whistle-daniel_simon.mp3': File contains data in an unknown format.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
================================================== 1 error in 11.87s ==================================================

[peterjc123]

Updated test results with PyTorch 1.3.1: https://gist.github.com/peterjc123/02f6cb8a00d8cdbc69b9adeb14a7c3ca

[vincentqb]

Thanks, I've updated the PR to get rid of more RuntimeError when sox is absent.

[cpuhrsch]

This seems like a regression in test coverage due to an OS specific need? Ideally we could detect the available backends at runtime.

[vincentqb]

This seems like a regression in test coverage due to an OS specific need?

All the tests that were running before this PR will still be running after. Currently, the CI on Windows is not active precisely because Windows only has SoundFile, and all the tests depending on SoX would fail.

(Some tests now use the wav version of the sample audio file instead of the mp3 version.)

Ideally we could detect the available backends at runtime.

The current mechanic to determine which backend is available is in torchaudio/_backend.py and runs at import time. We can indeed determine available backends at runtime. However, there is already a condition check for the platform to set the default backend.

[vincentqb]

@peterjc123 -- The windows build is failing, have you encountered this issue before? Could you also tell me if this new version of this PR reduced the number of failing tests in windows?

[vincentqb]

Linking #466 for general awareness

[mthrok]

LGTM.
Made some comments for readability improvement.

[mthrok]

The purpose of this function was not immediately clear to me at the first time reading it. Adding docstring would be helpful.

[vincentqb]

Thanks for pointing this out!

[mthrok]

The name of the module, _test, is not very descriptive.
Also, to me, prefixing with underscore does not give additional context, as test modules are never intended for external use. So, something like backend_utils sound more appropriate.

[vincentqb]

Good point. In fact, I'll just move those functions in common_utils.py :)