add nodepool webhook unit test

[luc99hen]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage
/sig storage

What this PR does / why we need it:

add np webhook unit test & complement np controller test

Which issue(s) this PR fixes:

Fixes #
#73

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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In response to this:

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage
/sig storage

What this PR does / why we need it:

add np webhook unit test & complement np controller test

Which issue(s) this PR fixes:

Fixes #
#73

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[luc99hen]

/assign @rambohe-ch

[codecov]

Codecov Report

Merging #97 (ac49250) into master (ffb2bc9) will increase coverage by 4.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #97      +/-   ##
==========================================
+ Coverage   21.21%   25.27%   +4.05%     
==========================================
  Files          21       25       +4     
  Lines        2550     2742     +192     
==========================================
+ Hits          541      693     +152     
- Misses       1932     1951      +19     
- Partials       77       98      +21     

Flag	Coverage Δ
unittests	25.27% <ø> (+4.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...manager/webhook/yurtingress/yurtingress_webhook.go	24.44% <0.00%> (ø)
...urtappmanager/webhook/nodepool/nodepool_webhook.go	40.42% <0.00%> (ø)
...ager/webhook/yurtingress/yurtingress_validating.go	46.15% <0.00%> (ø)
...appmanager/webhook/nodepool/nodepool_validation.go	37.50% <0.00%> (ø)
...manager/controller/nodepool/nodepool_controller.go	57.77% <0.00%> (+2.36%)	⬆️
...r/controller/nodepool/nodepool_enqueue_handlers.go	86.90% <0.00%> (+86.90%)	⬆️

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[rambohe-ch]

/lgtm
/approve

[openyurt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: luc99hen, rambohe-ch

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[huiwq1990]

@luc99hen it's better rebase master