test: add tests for pkg/app/client/retry/retry.go

[mamil]

What type of PR is this?

test: Adding missing tests or correcting existing tests
pkg/app/client/retry/retry.go test coverage reached 100%

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) Translate the PR title into Chinese.

为pkg/app/client/retry/retry.go添加测试

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

en: Add tests for pkg/app/client/retry/retry.go
zh(optional): 为pkg/app/client/retry/retry.go添加测试

Which issue(s) this PR fixes:

#257

[codecov]

Codecov Report

Base: 68.14% // Head: 68.29% // Increases project coverage by +0.15% 🎉

Coverage data is based on head (30109d0) compared to base (d39a818).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #419      +/-   ##
===========================================
+ Coverage    68.14%   68.29%   +0.15%     
===========================================
  Files           90       92       +2     
  Lines         8632     8686      +54     
===========================================
+ Hits          5882     5932      +50     
- Misses        2389     2393       +4     
  Partials       361      361              

Impacted Files	Coverage Δ
pkg/common/timer/timer.go	61.90% <0.00%> (-19.05%)	⬇️
pkg/app/client/retry/retry.go	100.00% <0.00%> (ø)
pkg/app/client/retry/option.go	100.00% <0.00%> (ø)

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[li-jin-gou]

LGTM