Add a general loc test

[Luni-4]

This PR adds a more general test for the Loc metric

It should be merged after #239

[codecov-commenter]

Codecov Report

Merging #254 into master will increase coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #254      +/-   ##
==========================================
+ Coverage   17.67%   17.70%   +0.02%     
==========================================
  Files          46       46              
  Lines        5963     5966       +3     
  Branches      707      708       +1     
==========================================
+ Hits         1054     1056       +2     
  Misses       4498     4498              
- Partials      411      412       +1     

Impacted Files	Coverage Δ
src/metrics/loc.rs	47.61% <66.66%> (+0.46%)	⬆️

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