Improved distributed tests

[arlesniak]

This PR fixes distributed tests in cases when an Exception raised in subprocess is not correctly manifested to pytest, finally reported as PASSED, causing false positive result.
Changes made:

• assert_run_mproc test utility function for decorating and running Processes
• MPCaptOutput context utility class, capturing std output and stderr

[codecov]

Codecov Report

Attention: Patch coverage is 36.84211% with 36 lines in your changes are missing coverage. Please review.

Project coverage is 89.15%. Comparing base (e697d26) to head (36af13e).

Files	Patch %	Lines
torch_geometric/testing/distributed.py	36.84%	36 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8978      +/-   ##
==========================================
- Coverage   89.87%   89.15%   -0.72%     
==========================================
  Files         468      469       +1     
  Lines       30054    30106      +52     
==========================================
- Hits        27010    26840     -170     
- Misses       3044     3266     +222     

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[jjpietrak]

LGTM, we might need to keep an eye on dist tests after this is merged

CI errors

[jjpietrak]

Notice: A new release of pip is available: 23.0.1 -> 24.0 Notice: To update, run: pip install --upgrade pip torch_geometric/testing/dist_utils.py:25: error: "TextIO" has no attribute "getvalue" [attr-defined] torch_geometric/testing/dist_utils.py:28: error: "TextIO" has no attribute "getvalue" [attr-defined] torch_geometric/testing/dist_utils.py:64: error: "Process" has no attribute "_target" [attr-defined] torch_geometric/testing/dist_utils.py:65: error: "Process" has no attribute "_target" [attr-defined] torch_geometric/testing/dist_utils.py:66: error: "Process" has no attribute "_args" [attr-defined]

@arlesniak we need to look into thos CI issues first

[kgajdamo]

Looks good to me

[rusty1s]

Amazing :)