refactor: increase post module coverage

[germa89]

Description

As the title.

Issue linked

close #3502

Checklist

• I have visited and read Develop PyMAPDL.
• I have tested my changes locally
• I have added necessary documentation or updated existing documentation.
• I have followed the PyMAPDL coding style guidelines.
• I have added appropriate unit tests that also ensure the minimal coverage criteria.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have marked this PR as draft if it is not ready to be reviewed yet.
• I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.64%. Comparing base (abcb5ae) to head (d43196d).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3556      +/-   ##
==========================================
+ Coverage   91.28%   91.64%   +0.35%     
==========================================
  Files         187      187              
  Lines       14638    14615      -23     
==========================================
+ Hits        13363    13394      +31     
+ Misses       1275     1221      -54     

---- 🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests

[germa89]

Increased 12.75% the coverage in the post module.

https://app.codecov.io/gh/ansys/pymapdl/pull/3556?dropdown=coverage&src=pr&el=h1&utm_medium=referral&utm_source=github&utm_content=checks&utm_campaign=pr+comments&utm_term=ansys

[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬