Add unit test

[suzuito]

https://github.com/suzuito/private/issues/626

[codecov-commenter]

Codecov Report

Merging #84 (d48066c) into main (8fe15bd) will increase coverage by 83.88%.
The diff coverage is 77.29%.

@@            Coverage Diff            @@
##           main      #84       +/-   ##
=========================================
+ Coverage      0   83.88%   +83.88%     
=========================================
  Files         0       24       +24     
  Lines         0      819      +819     
=========================================
+ Hits          0      687      +687     
- Misses        0      122      +122     
- Partials      0       10       +10     

Impacted Files	Coverage Δ
pkg/usecase/usecase_mock.go	0.00% <0.00%> (ø)
internal/bgin/handler_html_error.go	11.11% <50.00%> (ø)
internal/bgin/handler_html_robots.go	44.00% <66.66%> (ø)
pkg/usecase/storage_mock.go	78.94% <78.94%> (ø)
internal/bgin/router.go	82.75% <88.88%> (ø)
internal/bgin/handler_html_article.go	88.52% <90.90%> (ø)
internal/bgin/handler_html_about.go	100.00% <100.00%> (ø)
internal/bgin/handler_html_articles.go	88.52% <100.00%> (ø)
internal/bgin/handler_html_top.go	100.00% <100.00%> (ø)
internal/bgin/handler_xml_sitemap.go	42.85% <100.00%> (ø)
... and 29 more

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