pkg/analysis/messagefmt: add tests

[ldez]

Because tests are good 😸

[codecov]

Codecov Report

Merging #11 (8d9f470) into main (00ba86c) will increase coverage by 65.85%.
The diff coverage is 75.00%.

@@            Coverage Diff            @@
##           main      #11       +/-   ##
=========================================
+ Coverage      0   65.85%   +65.85%     
=========================================
  Files         0        1        +1     
  Lines         0       82       +82     
=========================================
+ Hits          0       54       +54     
- Misses        0       15       +15     
- Partials      0       13       +13     

Impacted Files	Coverage Δ
pkg/analysis/messagefmt/analyzer.go	65.85% <75.00%> (ø)

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