.NET: Improve unit test coverage for Microsoft.Agents.AI.AzureAI to 85.6%

[Copilot]

Motivation and Context

Unit test coverage for Microsoft.Agents.AI.AzureAI was at 64.5%, below the required 85% threshold.

Description

Added 30 new unit tests in AzureAIProjectChatClientExtensionsCoverageTests targeting uncovered code paths:

• Name validation: Empty/null/whitespace agent name handling in GetAIAgentAsync and CreateAIAgentAsync
• Response formats: ChatResponseFormatText, ChatResponseFormatJson with/without schema, strict mode
• RawRepresentationFactory: Null returns, CreateResponseOptions returns, non-matching types
• Tool validation: Missing required tools, partial tool provision, wrong tool names
• Options preservation: AIContextProviderFactory, ChatMessageStoreFactory, UseProvidedChatClientAsIs
• Tool conversion: ResponseTool.AsAITool(), hosted tools, mixed server tools

Also fixed net472 build compatibility by replacing ValueTask.CompletedTask with default.

Coverage results:

Component	Before	After
AzureAIProjectChatClientExtensions.cs	73.99%	90.08%
Overall Microsoft.Agents.AI.AzureAI	~64.5%	85.6%

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? No

Original prompt

---

This section details on the original issue you should resolve

<issue_title>.NET: Improve unit test coverage for Microsoft.Agents.AI.AzureAI</issue_title>
<issue_description>Required level is 85%, current level is 64.5%

</issue_description>

<agent_instructions>Please analyze the Cobertura Coverage information related to the Microsoft.Agents.AI.AzureAI and lets improve its coverage on non-covered paths.

Please keep the same patterns used for UnitTests existing into the Microsoft.Agents.AI.AzureAI.UnitTests.

Use our repository guidelines regarding UnitTests code as well as use our existing File approach for the UnitTests generatino, only creating new ones if the file being covered have not being covered yet.

Ensure the coverage only covers non-covered paths without duplicating paths that are already covered.

Ensure all existing tests are working on top of the new added ones. This change should only be focused in UnitTests not changing any functionality.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes .NET: Improve unit test coverage for Microsoft.Agents.AI.AzureAI #3337

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[rogerbarreto]

@copilot

Address below with the project

Error: /home/runner/work/agent-framework/agent-framework/dotnet/tests/Microsoft.Agents.AI.AzureAI.UnitTests/AzureAIProjectChatClientExtensionsTests.cs(3164,30): error CS0117: 'ValueTask' does not contain a definition for 'CompletedTask' [/home/runner/work/agent-framework/agent-framework/dotnet/tests/Microsoft.Agents.AI.AzureAI.UnitTests/Microsoft.Agents.AI.AzureAI.UnitTests.csproj::TargetFramework=net472] (potentially using default may resolve)