Improve test environment for artifact tests

[MariusStorhaug]

Context

The artifact tests in tests/Artifacts.Tests.ps1 are used to verify that artifact retrieval and management functions work correctly. These tests run as part of the module's CI/CD pipeline in GitHub Actions.

Request

The current artifact tests depend on environment variables and real artifacts from the CI/CD pipeline:

$Owner = $env:GITHUB_REPOSITORY_OWNER
$Repository = $env:GITHUB_REPOSITORY_NAME
$WorkflowRunId = $env:GITHUB_RUN_ID
$ArtifactName = 'module'

This approach has several limitations:

1. Dependency on real data — tests depend on artifacts actually existing from the current workflow run
2. Brittle tests — if artifacts are deleted or workflow structure changes, tests may fail
3. Limited test scenarios — can only test against whatever artifacts happen to exist
4. CI/CD coupling — tests are tightly coupled to the pipeline state, making them difficult to run locally or in isolation

What is expected

A dedicated test environment for artifact tests that enables predictable, isolated testing with controlled test data.

Acceptance criteria

• Artifact tests use predictable test data with known properties
• Tests can cover edge cases and error scenarios (empty artifacts, large artifacts, missing artifacts)
• Tests are not brittle due to external state changes
• Test setup is documented

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Technical decisions

Test data strategy: Use a dedicated test workflow or the BeforeAll.ps1 setup script to generate artifacts with predictable names and properties before the artifact tests run. This keeps the tests self-contained while still testing against real GitHub API behavior.

Integration vs unit tests: Keep tests as integration tests (calling real API endpoints) since the primary value is verifying the API interaction. Mock-based unit tests would not catch issues with artifact response parsing or pagination.

Alignment with #534: This issue aligns with the broader test consolidation effort in #534. The artifact tests should follow the same patterns established there (top-level BeforeAll, $env:GITHUB_RUN_ID as identifier, standard auth case structure).

Test approach: Update tests/Artifacts.Tests.ps1 to follow the standard test pattern from #534, using $env:GITHUB_REPOSITORY_* variables for the current repo (which is the unique pattern for artifact tests since artifacts are tied to the current workflow run).

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Implementation plan

• Update tests/Artifacts.Tests.ps1 to use the standard test pattern (top-level BeforeAll, auth cases, skip conditions)
• Ensure the artifact test setup creates or identifies predictable test artifacts
• Add tests for edge cases: non-existent artifact name, artifact from a specific workflow run
• Document the test data setup and requirements in the test file or test README

[MariusStorhaug]

Restructured issue description into the standard three-section format.

• Rewrote context and request to describe the test reliability problem from the developer's perspective
• Added technical decisions covering test data strategy, integration vs unit testing, alignment with Consolidate test setup/teardown tasks #534
• Created implementation plan with 4 tasks
• Updated title (removed emoji prefix), applied Patch label, set issue type to Task