test: improve ut coverage

[cvvz]

What type of PR is this?

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

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none

[cvvz]

/retest

[k8s-ci-robot]

@cvvz: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-azurefile-csi-driver-e2e-capz	8337ff8	link	true	/test pull-azurefile-csi-driver-e2e-capz

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[andyzhangx]

/retest
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andyzhangx, cvvz

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