test: add more unit tests

[AlexD10S]

Add some more unit tests to improve the coverage.

[codecov]

Codecov Report

Attention: Patch coverage is 83.67347% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 47.94%. Comparing base (85353ae) to head (ddbeeee).

@@            Coverage Diff             @@
##             main     #161      +/-   ##
==========================================
+ Coverage   47.07%   47.94%   +0.87%     
==========================================
  Files          32       32              
  Lines        2649     2680      +31     
  Branches     2649     2680      +31     
==========================================
+ Hits         1247     1285      +38     
+ Misses       1214     1197      -17     
- Partials      188      198      +10     

Files	Coverage Δ
crates/pop-parachains/src/generator/parachain.rs	0.00% <ø> (ø)
crates/pop-cli/src/main.rs	14.42% <90.00%> (+9.37%)	⬆️
crates/pop-parachains/src/utils/helpers.rs	79.77% <90.00%> (+2.96%)	⬆️
crates/pop-parachains/src/utils/git.rs	42.02% <73.68%> (+1.92%)	⬆️