[C#] feat: add unit test for models (#1187)

## Linked issues

#minor: partial of #907

## Details

Provide a list of your changes here. If you are fixing a bug, please
provide steps to reproduce the bug.

#### Change details

> Describe your changes, with screenshots and code snippets as
appropriate

**code snippets**:

**screenshots**:

## Attestation Checklist

- [x] My code follows the style guidelines of this project

- I have checked for/fixed spelling, linting, and other errors
- I have commented my code for clarity
- I have made corresponding changes to the documentation (we use
[TypeDoc](https://typedoc.org/) to document our code)
- My changes generate no new warnings
- I have added tests that validates my changes, and provides sufficient
test coverage. I have tested with:
  - Local testing
  - E2E testing in Teams
- New and existing unit tests pass locally with my changes

### Additional information

> Feel free to add other relevant information below

dotnet/packages/Microsoft.TeamsAI/Microsoft.TeamsAI.Tests/AITests/Models/ChatMessageExtensionsTests.cs

@@ -0,0 +1,31 @@
+using Microsoft.Teams.AI.AI.Models;
+
+namespace Microsoft.Teams.AI.Tests.AITests.Models
+{
+    public class ChatMessageExtensionsTests
+    {
+        [Fact]
+        public void Test_ToAzureSdkChatMessage()
+        {
+            // Arrange
+            var chatMessage = new ChatMessage(ChatRole.User)
+            {
+                Name = "test-name",
+                Content = "test-content",
+            };
+
+            // Act
+            var result1 = chatMessage.ToAzureSdkChatMessage();
+            chatMessage.FunctionCall = new FunctionCall("test-name", "test-args");
+            var result2 = chatMessage.ToAzureSdkChatMessage();
+
+            // Assert
+            Assert.Equal(Azure.AI.OpenAI.ChatRole.User, result1.Role);
+            Assert.Equal("test-name", result1.Name);
+            Assert.Equal("test-content", result1.Content);
+            Assert.Null(result1.FunctionCall);
+            Assert.Equal("test-name", result2.FunctionCall.Name);
+            Assert.Equal("test-args", result2.FunctionCall.Arguments);
+        }
+    }
+}

dotnet/packages/Microsoft.TeamsAI/Microsoft.TeamsAI.Tests/AITests/Models/ChatRoleTests.cs

@@ -0,0 +1,92 @@
+using Microsoft.Teams.AI.AI.Models;
+
+namespace Microsoft.Teams.AI.Tests.AITests.Models
+{
+    public class ChatRoleTests
+    {
+        [Fact]
+        public void Test_Constructor_ArgumentNullException()
+        {
+            // Arrange
+            string? role = null;
+
+            // Act
+            var exception = Assert.Throws<ArgumentNullException>(() => new ChatRole(role!));
+
+            // Assert
+            Assert.NotNull(exception);
+        }
+
+        [Fact]
+        public void Test_OperatorEquality()
+        {
+            // Arrange
+            var chatRole1 = new ChatRole("user");
+            var chatRole2 = ChatRole.User;
+            var chatRole3 = ChatRole.Assistant;
+
+            // Act
+            var result1 = chatRole1 == chatRole2;
+            var result2 = chatRole1 == chatRole3;
+            var result3 = chatRole2 != chatRole3;
+
+            // Assert
+            Assert.True(result1);
+            Assert.False(result2);
+            Assert.True(result3);
+        }
+
+        [Fact]
+        public void Test_Equals()
+        {
+            // Arrange
+            var chatRole1 = new ChatRole("user");
+            var chatRole2 = ChatRole.User;
+            var chatRole3 = ChatRole.Assistant;
+
+            // Act
+            var result1 = chatRole1.Equals(chatRole2);
+            var result2 = chatRole1.Equals(chatRole3);
+
+            // Assert
+            Assert.True(result1);
+            Assert.False(result2);
+        }
+
+        [Fact]
+        public void Test_ToString()
+        {
+            // Arrange
+            var chatRole = new ChatRole("test");
+
+            // Act
+            var result = chatRole.ToString();
+
+            // Assert
+            Assert.Equal("test", result.ToString());
+        }
+
+        [Fact]
+        public void Test_ImplicitConversion()
+        {
+            // Arrange
+            ChatRole chatRole = "user";
+
+            // Assert
+            Assert.Equal("user", chatRole.Value);
+        }
+
+        [Fact]
+        public void Test_GetHashCode()
+        {
+            // Arrange
+            var chatRole = ChatRole.Function;
+
+            // Act
+            var result = chatRole.GetHashCode();
+
+            // Assert
+            Assert.Equal("function".GetHashCode(), result);
+        }
+    }
+}

dotnet/packages/Microsoft.TeamsAI/Microsoft.TeamsAI.Tests/AITests/OpenAIModelTests.cs → dotnet/packages/Microsoft.TeamsAI/Microsoft.TeamsAI.Tests/AITests/Models/OpenAIModelTests.cs

@@ -14,7 +14,7 @@
 using ChatMessage = Microsoft.Teams.AI.AI.Models.ChatMessage;
 using ChatRole = Microsoft.Teams.AI.AI.Models.ChatRole;
 
-namespace Microsoft.Teams.AI.Tests.AITests
+namespace Microsoft.Teams.AI.Tests.AITests.Models
 {
     public class OpenAIModelTests
     {

dotnet/packages/Microsoft.TeamsAI/Microsoft.TeamsAI.Tests/AITests/Models/SequentialDelayStrategyTests.cs

@@ -0,0 +1,45 @@
+using Azure;
+using Microsoft.Teams.AI.AI.Models;
+
+namespace Microsoft.Teams.AI.Tests.AITests.Models
+{
+    public class SequentialDelayStrategyTests
+    {
+        [Fact]
+        public void Test_SequentialDelayStrategy()
+        {
+            // Arrange
+            var delays = new List<TimeSpan>()
+            {
+                TimeSpan.FromMilliseconds(1000),
+                TimeSpan.FromMilliseconds(2000),
+                TimeSpan.FromMilliseconds(3000),
+            };
+            var strategy = new TestSequentialDelayStrategy(delays);
+
+            // Act
+            var result1 = strategy.GetNextDelayCoreMethod(null, 1);
+            var result2 = strategy.GetNextDelayCoreMethod(null, 2);
+            var result3 = strategy.GetNextDelayCoreMethod(null, 3);
+            var result4 = strategy.GetNextDelayCoreMethod(null, 4);
+
+            // Assert
+            Assert.Equal(TimeSpan.FromMilliseconds(1000), result1);
+            Assert.Equal(TimeSpan.FromMilliseconds(2000), result2);
+            Assert.Equal(TimeSpan.FromMilliseconds(3000), result3);
+            Assert.Equal(TimeSpan.FromMilliseconds(3000), result4);
+        }
+    }
+
+    internal class TestSequentialDelayStrategy : SequentialDelayStrategy
+    {
+        public TestSequentialDelayStrategy(List<TimeSpan> delays) : base(delays)
+        {
+        }
+
+        public TimeSpan GetNextDelayCoreMethod(Response? response, int retryNumber)
+        {
+            return base.GetNextDelayCore(response, retryNumber);
+        }
+    }
+}