tests: Add a test-only init for issue 2448

[georgebisbas]

As discussed in the weekly meeting 24th of Sept.

https://github.com/devitocodes/devito/issues/2448

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 14.28571% with 24 lines in your changes missing coverage. Please review.

Project coverage is 78.70%. Comparing base (74f3496) to head (a09dfc4). Report is 25 commits behind head on master.

Files with missing lines	Patch %	Lines
tests/test_mpi.py	14.28%	24 Missing :warning:

:exclamation: There is a different number of reports uploaded between BASE (74f3496) and HEAD (a09dfc4). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (74f3496)	HEAD (a09dfc4)
	16	14

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2465      +/-   ##
==========================================
- Coverage   87.06%   78.70%   -8.37%     
==========================================
  Files         239      239              
  Lines       45123    45151      +28     
  Branches     8428     8430       +2     
==========================================
- Hits        39286    35535    -3751     
- Misses       5102     8825    +3723     
- Partials      735      791      +56     

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[georgebisbas]

Closing in favor of #2477