Improve unit test coverage across multiple packages

[Copilot]

This PR improves unit test coverage across several packages in the azuredisk-csi-driver repository to help reach the target of 85% coverage from the current ~82%.

Key Improvements

Package Coverage Improvements

• mounter: 85.7% → 97.1% (+11.4%)
• azurediskplugin: 28.0% → 40.0% (+12.0%)
• azuredisk: Added tests for previously uncovered functions
• tool: Enhanced function-level coverage for utility functions
• test/utils/credentials: Added additional test coverage

New Test Coverage Areas

Critical Function Tests Added

• TestIsCheckDiskLunThrottled: Tests cache throttling functionality in azuredisk package
• TestGetOccupiedLunsFromNode: Tests LUN collision detection logic
• TestRescanVolume: Tests device rescanning functionality on Linux
• TestIsMountPoint: Tests mount point detection in mounter package
• TestExportMetrics: Tests metrics export functionality in azurediskplugin
• TestDeleteAzureCredentialFile: Tests credential file cleanup

Utility Function Tests

• TestFormatInt: Tests integer formatting utility
• TestAppendWithErrCheck: Tests string builder error handling
• TestGetAllSkus: Tests SKU retrieval functionality

Technical Details

All new tests follow existing patterns and use appropriate mocking where necessary. The tests focus on:

1. Error path coverage: Testing both success and failure scenarios
2. Edge case handling: Testing boundary conditions and invalid inputs
3. Core functionality: Testing critical driver operations like LUN management and mount operations
4. Utility functions: Improving coverage of helper functions

Testing

# Run all unit tests
make unit-test

# Check coverage for specific packages
go test -cover ./pkg/mounter
go test -cover ./pkg/azurediskplugin

The changes maintain backward compatibility and don't modify existing functionality - only adding comprehensive test coverage for previously untested code paths.

Fixes #1424.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• login.microsoftonline.com
  • Triggering command: /tmp/go-build1611419854/b1191/azuredisk.test -test.testlogfile=/tmp/go-build1611419854/b1191/testlog.txt -test.paniconexit0 -test.gocoverdir=/tmp/go-build1611419854/b1191/gocoverdir -test.timeout=10m0s -test.v=true (dns block)
  • Triggering command: /tmp/go-build3361430853/b1191/azuredisk.test -test.paniconexit0 -test.gocoverdir=/tmp/go-build3361430853/b1191/gocoverdir -test.timeout=10m0s -test.v=true -test.coverprofile=/tmp/go-build3361430853/b1191/_cover_.out (dns block)
  • Triggering command: /tmp/go-build238207495/b1191/azuredisk.test -test.testlogfile=/tmp/go-build238207495/b1191/testlog.txt -test.paniconexit0 -test.gocoverdir=/tmp/go-build238207495/b1191/gocoverdir -test.timeout=10m0s -test.v=true (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

---

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[linux-foundation-easycla]

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[k8s-ci-robot]

Hi @Copilot. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Copilot
Once this PR has been reviewed and has the lgtm label, please ask for approval from andyzhangx. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

PR needs rebase.

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-sigs/prow repository.