Refactor run_tests subprocess usage

[aobolensk]

• update __run_exec to take argument lists
• pass argument lists instead of command strings

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.37%. Comparing base (81c3284) to head (9b4f55b).
Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #450   +/-   ##
=======================================
  Coverage   92.37%   92.37%           
=======================================
  Files          11       11           
  Lines         354      354           
  Branches      124      124           
=======================================
  Hits          327      327           
  Misses         10       10           
  Partials       17       17           

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