test: enable parallelism, add NSubstitute, document test infrastructure (TEST-M4, H1)

[laurentiu021]

Summary

Addresses test quality findings TEST-M4 and TEST-H1 from the full review.

Changes

TEST-M4: Enable test parallelism

• Changed xunit.runner.json: parallelizeTestCollections true, maxParallelThreads 0 (auto)
• Tests using shared OS resources remain serialized via [Collection] attributes
• Reduced longRunningTestSeconds from 120 to 30 for faster flaky detection

TEST-H1: Add mocking framework

• Added NSubstitute 5.3.0 to the test project
• Enables interface-based mocking for future tests that need to isolate OS dependencies
• No existing tests modified — this is infrastructure for new tests going forward

Documentation

• Updated TESTING.md with test infrastructure section (frameworks table, parallelism strategy, conventions)

Note

This is a test: commit — no release triggered. TEST-H2 (coverage gaps), TEST-M1 (flaky tests), and TEST-M2 (thread-safety assertions) are tracked in issue #320 for incremental improvement.

Testing

• Build: 0 errors (tests project compiles with NSubstitute)

Summary by CodeRabbit

• Documentation

  • Added test infrastructure documentation covering frameworks, parallelization strategy, and testing best practices.

• Chores

  • Optimized test execution speed through enhanced parallel processing configuration.
  • Updated testing framework dependencies to the latest versions.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 7841042e-3769-4118-9505-02ec6543d0d3

📥 Commits

Reviewing files that changed from the base of the PR and between c6c335b and 1c95865.

📒 Files selected for processing (4)

• CHANGELOG.md
• SysManager/SysManager.Tests/SysManager.Tests.csproj
• SysManager/SysManager.Tests/xunit.runner.json
• TESTING.md

📜 Recent review details

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: Build & unit tests
• GitHub Check: Analyze (csharp)

🔇 Additional comments (4)

SysManager/SysManager.Tests/xunit.runner.json (1)

3-5: LGTM!

SysManager/SysManager.Tests/SysManager.Tests.csproj (1)

16-16: LGTM!

TESTING.md (1)

52-77: LGTM!

CHANGELOG.md (1)

9-20: LGTM!

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📝 Walkthrough

Walkthrough

The PR enables xUnit test collection parallelization, adds NSubstitute 5.3 to test dependencies, adjusts test runner configuration thresholds, and documents the test infrastructure setup and testing conventions.

Changes

Test Infrastructure Configuration and Documentation

Layer / File(s)	Summary
Test parallelization and NSubstitute dependency SysManager/SysManager.Tests/xunit.runner.json, SysManager/SysManager.Tests/SysManager.Tests.csproj	xUnit runner configuration enables parallelizeTestCollections, sets maxParallelThreads to 0 (unlimited), and reduces longRunningTestSeconds to 30. NSubstitute 5.3.0 is added as a test project package reference.
Test infrastructure and changelog documentation TESTING.md, CHANGELOG.md	TESTING.md documents test frameworks, explains collection-based parallelism with isolation for resource-sharing tests, and lists testing conventions for speed and determinism. CHANGELOG.md records version 0.48.31 with notes on parallelism enabling, NSubstitute addition, and TESTING.md documentation.

Possibly Related PRs

• laurentiu021/SystemManager#368: Applies [Collection("OperationLock")] attributes to specific tests to ensure they are isolated under the parallel execution model enabled in this PR.

Estimated Code Review Effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 hop hop – tests in parallel we go,
NSubstitute mocks make chaos flow,
Collections grouped, no races to know,
Config and docs together grow! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately captures the three main changes: enabling test parallelism, adding NSubstitute dependency, and documenting test infrastructure, making it clear and specific to the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/test-quality

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Codecov Report

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