test: add ut for hertz/pkg/common/adaptor

[L2ncE]

What type of PR is this?

test

Check the PR title.

• This PR title match the format: <type>(optional scope): <description>
• The description of this PR title is user-oriented and clear enough for others to understand.

(Optional) More detail description for this PR(en: English/zh: Chinese).

en: add ut for hertz/pkg/common/adaptor, coverage increased from 76.6% to 92.3%
zh(optional): 增加对hertz/pkg/common/adaptor的单测，覆盖率从76.6%提高到了92.3%

Which issue(s) this PR fixes:

#257

[codecov]

Codecov Report

Base: 59.17% // Head: 59.26% // Increases project coverage by +0.08% 🎉

Coverage data is based on head (2a71ba0) compared to base (ea2569a).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #264      +/-   ##
===========================================
+ Coverage    59.17%   59.26%   +0.08%     
===========================================
  Files           79       79              
  Lines         8150     8150              
===========================================
+ Hits          4823     4830       +7     
+ Misses        2972     2967       -5     
+ Partials       355      353       -2     

Impacted Files	Coverage Δ
pkg/common/adaptor/response.go	94.59% <0.00%> (+18.91%)	⬆️

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[li-jin-gou]

It is forbidden to add a test only for the purpose of coverage but without logical meaning.

refer to issue description #257

[welkeyever]

Thanks！lgtm