ci: Cache datasets

[akihironitta]

What does this PR do?

Fixes #279. All tests now use ./datasets/ to store downloaded datasets and to restore from if already downloaded.

Description of the changes

• GitHub Actions
  • Add Cache datasets section
• pytest
  • Remove unused tmpdir fixture
  • Create tests/conftest.py to define data_dir and DATA_DIR which can be referenced from each test.
    • data_dir fixture can be used without any import in each test.
    • DATA_DIR const variable is defined to refer to the dataset directory in pytest.mark.parametrize(). pytest does not support using fixtures in pytest.mark.parametrize(). See Using fixtures in pytest.mark.parametrize pytest-dev/pytest#349.

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[codecov]

Codecov Report

Merging #315 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #315      +/-   ##
==========================================
+ Coverage   82.37%   82.39%   +0.01%     
==========================================
  Files          99       99              
  Lines        5612     5611       -1     
==========================================
  Hits         4623     4623              
+ Misses        989      988       -1     

Flag	Coverage Δ
cpu	24.62% <0.00%> (-0.02%)	⬇️
pytest	24.62% <0.00%> (-0.02%)	⬇️
unittests	81.78% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pl_bolts/models/mnist_module.py	100.00% <100.00%> (ø)
pl_bolts/datasets/cifar10_dataset.py	97.87% <0.00%> (+1.06%)	⬆️

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[pep8speaks]

Hello @akihironitta! Thanks for updating this PR.

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2020-11-06 13:16:11 UTC

[akihironitta]

https://github.com/PyTorchLightning/pytorch-lightning-bolts/blob/6c51b4cd975ef0f03d1e7210111ded43e4b07d91/.github/workflows/ci_test-full.yml#L81
Is it better to create a script to download datasets and specify it here?

[akihironitta]

I am not sure if the way of caching datasets is originally expected in the linked issue. If I am doing something which you find unreasonable, please let me know and close this PR! (It was a great opportunity to look through docs of actions/cache and pytest :])

[Borda]

Nice, btw have you tested that DataModules really does not create any other folder?