L0 functional coverage for DownloadPackageV1, and NuGetToolInstaller (V0/V1)

[AlexVTor]

Context

Describe the context or motivation for this PR. Include links to any related Azure DevOps Work Items or GitHub issues.
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Task Name

NpmV1
DownloadPackageV1
NuGetToolInstallerV0
NuGetToolInstallerV1

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Description

• Expands L0 coverage across NuGetV0, DownloadPackageV1, NuGetToolInstallerV0, and NuGetToolInstallerV1 with emphasis on functional behavior (eg: branching, routing, command/tool invocation, and failure paths).
• Refactors NuGetV0 version-threshold logic into a small helper and adds unit-style L0 tests for logic.
• Adds unit-style L0 tests for DownloadPackageV1 retry/backoff behavior and package-builder routing/mapping behavior.
• Strengthens installer L0 assertions to verify branch exclusivity (explicit vs default/resolved version paths) and failure short-circuit behavior.
• Keeps changes scoped to tests and low-risk helper extraction; no intended runtime behavior changes.

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Risk Assessment (Low / Medium / High)

Low - Runtime behavior has not been changed

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Change Behind Feature Flag (Yes / No)

N - Tests cannot be gated behind FF

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Tech Design / Approach

• Design has been written and reviewed.
• Any architectural decisions, trade-offs, and alternatives are captured.
  N/A

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Documentation Changes Required (Yes/No)

Indicate whether related documentation needs to be updated.

• User guides, API specs, system diagrams, or runbooks are updated.
  N/A

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Unit Tests Added or Updated (Yes / No)

Indicate whether unit tests were added or modified to reflect these changes.
Y

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Additional Testing Performed

List all other tests performed (manual or automated, including integration, regression, scenario tests, etc.).

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Logging Added/Updated (Yes/No)

• Appropriate log statements are added with meaningful messages.
• Logging does not expose sensitive data.
• Log levels are used correctly (e.g., info, warn, error).
  Y

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Telemetry Added/Updated (Yes/No)

• Custom telemetry (e.g., counters, timers, error tracking) is added as needed.
• Events are tagged with proper metadata for filtering and analysis.
• Telemetry is validated in staging or test environments.
  Y

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Rollback Scenario and Process (Yes/No)

• Rollback plan is documented.
  Rollback via taskoverride can be applied

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Dependency Impact Assessed and Regression Tested (Yes/No)

• All impacted internal modules, APIs, services, and third-party libraries are analyzed.
• Results are reviewed and confirmed to not break existing functionality.

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Checklist

• Related issue linked (if applicable)
• Task version was bumped — see versioning guide
• Verified the task behaves as expected

[AlexVTor]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[AlexVTor]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[AlexVTor]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[AlexVTor]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[AlexVTor]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).