chore: test coverage improvement

[VictorAssunc]

I noticed that some functions and function aliases weren't being completely covered by the tests, so I decided to create and improve some tests.

I decided to separate by commits instead of PRs to not spam the repository.

I'm not sure if I chose the best approach in each test, so I'm willing to change and learn more :)

[samber]

hi @VictorAssunc and thanks for this first contrib

i made 1 comment

CI runs tests with make test.

[codecov-commenter]

Codecov Report

Base: 98.50% // Head: 99.57% // Increases project coverage by +1.06% 🎉

Coverage data is based on head (040da80) compared to base (3206009).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #240      +/-   ##
==========================================
+ Coverage   98.50%   99.57%   +1.06%     
==========================================
  Files          16       16              
  Lines        1871     1871              
==========================================
+ Hits         1843     1863      +20     
+ Misses         26        8      -18     
+ Partials        2        0       -2     

Flag	Coverage Δ
unittests	99.57% <ø> (+1.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
errors.go	99.50% <0.00%> (+0.98%)	⬆️
slice.go	100.00% <0.00%> (+2.14%)	⬆️
map.go	100.00% <0.00%> (+3.30%)	⬆️
channel.go	97.53% <0.00%> (+4.32%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[samber]

I removed the parallel execution when you use a custom rand seed ;)