add unit test for GetMsgByCode

[zhouhao3]

Signed-off-by: Zhou Hao [email protected]

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)? (你真的觉得不需要加测试吗？)

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[pouchrobot]

We found this is your first time to contribute to Dragonfly, @q384566678
👏 We really appreciate it.
Just remind that you have read the contribution guide: https://github.com/dragonflyoss/Dragonfly/blob/master/CONTRIBUTING.md
If you didn't, you should do that first. If done, welcome again and please enjoy hacking! 🍻

[codecov-io]

Codecov Report

Merging #1179 into master will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #1179      +/-   ##
=========================================
+ Coverage   47.47%   47.6%   +0.12%     
=========================================
  Files         113     114       +1     
  Lines        7193    7212      +19     
=========================================
+ Hits         3415    3433      +18     
- Misses       3505    3506       +1     
  Partials      273     273

Impacted Files	Coverage Δ
pkg/constants/dfget_super_code.go	94.73% <0%> (ø)

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[lowzj]

LGTM