[WIP] Monkeypatch tests

[ritiek]

This PR mainly monkeypatches some of our tests, especially the ones that search on YouTube (these have been failing very frequently).

Changes:

• test_with_metadata.py now makes tests on this track https://open.spotify.com/track/3SipFlNddvL0XNZRLXvdZD (Janji - Heroes). I've saved the HTML content from this track's YouTube's search results to this Gist. It would fetch the raw content of this gist in the tests test_with_metadata.{test_youtube_url, test_youtube_title}. Yipee!!

• Also monkeypatched Pafy.download in our tests, so we don't eat heavy network resources. Instead, this call now either generates 1 sec blank audio (using FFmpeg) or does nothing depending on whether we need to perform further operations (like embedding metadata) on the track.

• The function convert.song now also returns the FFmpeg command which was invoked to conversion.

• youtube_tools.generate_m3u now returns a list of YouTube video URLs it wrote in the .m3u file.

• Some minor grammatical changes in variable and function names.

• Moved test cases from test_list.py to test_spotify_tools.py and test_youtube_tools.py as appropriate.

• Change FFmpeg to use the built-in encoder aac instead of 3rd party libfdk-aac which does not ship with the apt package (we might as well just be able to sudo apt install ffmpeg in .travis.yml!).

However, there are a couple of more ideas I have for this PR like skipping FFmpeg tests if the user doesn't have it installed and if anything else interesting comes to me, so let's wait a bit before merging this.

EDIT: Let's just keep it mandatory to install FFmpeg instead of skipping tests. Skipping tests = no good.

[ritiek]

I don't know what else we might want to monkeypatch for now. The tests seem to be passing on Travis with this PR! In case the other tests fail in the future (the ones not monkeypatched) due to dynamic web content, we could probably monkeypatch them at that time in the future.

[ritiek]

Note to self: Fix these warnings showing up on Travis:

test/test_with_metadata.py::test_youtube_url
  /home/travis/build/ritiek/spotify-downloader/spotdl/youtube_tools.py:158: RemovedInPytest4Warning: Fixture "monkeypatch_youtube_search_page" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    url = url_fetch.scrape()
test/test_with_metadata.py::test_youtube_title
  /home/travis/build/ritiek/spotify-downloader/spotdl/youtube_tools.py:158: RemovedInPytest4Warning: Fixture "monkeypatch_youtube_search_page" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    url = url_fetch.scrape()

EDIT: Done!

[ritiek]

The code should be ready for review (hella lot of changes I know :). I'll update CHANGES.md soon.

[linusg]

Awesome! Really lots of changes, so I may have missed something. But except for some indentations black would handle differently, this LGTM 👍

[linusg]

Also, fetching the HTML from a Gist is pretty neat! 😄

[ritiek]

Thanks for the review @linusg! I'll merge this. The master branch certainly needs some passing builds! :D

[linusg]

The master branch certainly needs some passing builds! :D

Yes indeed!

✅ https://travis-ci.org/ritiek/spotify-downloader/builds/472316484