feat(pkg.model) add model unit test

[wang1309]

…-db/arana/issues/778

What this PR does:
add model unit test

Which issue(s) this PR fixes:

Fixes #778

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[cr-gpt]

Seems you are using me but didn't get OPENAI_API_KEY seted in Variables/Secrets for this repo. you could follow readme for more information

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
5 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (108fb12) 40.33% compared to head (d743cb0) 40.47%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #802      +/-   ##
==========================================
+ Coverage   40.33%   40.47%   +0.13%     
==========================================
  Files         265      265              
  Lines       26711    26711              
==========================================
+ Hits        10775    10812      +37     
+ Misses      14782    14736      -46     
- Partials     1154     1163       +9     

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