Add test infrastructure for agent conformance tests (#77)

* Add test infrastructure for agent conformance tests

* Address PR comments.

* Switch TargetFrameworks to have inline condition

dotnet/tests/OpenAIChatCompletion.IntegrationTests/OpenAIChatCompletionFixture.cs

@@ -0,0 +1,55 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using AgentConformance.IntegrationTests;
+using AgentConformanceTests;
+using Microsoft.Agents;
+using Microsoft.Extensions.AI;
+using OpenAI;
+
+namespace OpenAIChatCompletion.IntegrationTests;
+
+public class OpenAIChatCompletionFixture : AgentFixture
+{
+#pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring as nullable.
+    private IChatClient _chatClient;
+    private Agent _agent;
+    private AgentThread _agentThread;
+#pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring as nullable.
+
+    public override Agent Agent => this._agent;
+
+    public override AgentThread AgentThread => this._agentThread;
+
+    public override Task<List<ChatMessage>> GetChatHistory()
+    {
+        throw new System.NotImplementedException();
+    }
+
+    public override Task InitializeAsync()
+    {
+        var config = TestConfiguration.LoadSection<OpenAIConfiguration>();
+
+        this._chatClient = new OpenAIClient(config.ApiKey)
+            .GetChatClient(config.ChatModelId)
+            .AsIChatClient();
+
+        this._agentThread = new ChatClientAgentThread();
+
+        this._agent =
+            new ChatClientAgent(this._chatClient, new()
+            {
+                Name = "HelpfulAssistant",
+                Instructions = "You are a helpful assistant.",
+            });
+
+        return Task.CompletedTask;
+    }
+
+    public override Task DisposeAsync()
+    {
+        this._chatClient.Dispose();
+        return Task.CompletedTask;
+    }
+}