test: add test for pkg/app

[chaoranz758]

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.
• Attach the PR updating the user documentation if the current PR requires user awareness at the usage level. User docs repo.

(Optional) Translate the PR title into Chinese.

提升pkg/app的单元测试覆盖率

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

en:Supplement unit test for pkg/app from 70.87% to 84.8%
zh(optional):提升pkg/app的单元测试覆盖率70.87%到84.8%

(Optional) Which issue(s) this PR fixes:

part of #257

(Optional) The PR that updates user documentation:

[welkeyever]

Better add some info - including the coverage changes - in the description of PR.

[chaoranz758]

Better add some info - including the coverage changes - in the description of PR.

done

[codecov]

Codecov Report

Patch coverage: 71.42% and project coverage change: +1.67% 🎉

Comparison is base (a3770c3) 80.30% compared to head (a5a58ef) 81.97%.
Report is 4 commits behind head on develop.

❗ Current head a5a58ef differs from pull request most recent head 99b1dbe. Consider uploading reports for the commit 99b1dbe to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #863      +/-   ##
===========================================
+ Coverage    80.30%   81.97%   +1.67%     
===========================================
  Files           97       97              
  Lines         9602     9604       +2     
===========================================
+ Hits          7711     7873     +162     
+ Misses        1408     1258     -150     
+ Partials       483      473      -10     

Files Changed	Coverage Δ
pkg/protocol/http1/ext/common.go	70.32% <66.66%> (+0.19%)	⬆️
pkg/common/utils/chunk.go	93.93% <100.00%> (ø)

... and 11 files with indirect coverage changes

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[welkeyever]

LGTM, thx~