Remove subprocess calls from tests

[Sparks29032]

New tests from #249 and #250 give errors on Windows. Running as shell command (in the case of Windows) is not recommended.

We don't need to call the subprocess since we can directly simulate a CLI call similar to the tests already present in test_morphapp.py.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.92%. Comparing base (fc50526) to head (22f5ae3).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #251 +/- ##
=======================================
Coverage 99.92% 99.92% =======================================
Files 23 23 Lines 1354 1354 =======================================
Hits 1353 1353 Misses 1 1 

Files with missing lines	Coverage Δ
tests/test_morphsqueeze.py	100.00% <100.00%> (ø)
tests/test_refine.py	100.00% <100.00%> (ø)

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[Sparks29032]

Merging since this is the exact same set of tests, but without explicit subprocess calls. Refer to test_morphapp.py tests.

[sbillinge]

yes, this is much better. It is also possible to import the main function from the entry-point app and run that the desired inputs. This is how we would normally do it to be platform independent.