diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/MockAgentProvider.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/MockAgentProvider.cs
index 22438e2c6e..5a55dd297a 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/MockAgentProvider.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/MockAgentProvider.cs
@@ -40,6 +40,12 @@ public MockAgentProvider()
                 It.IsAny<bool>(),
                 It.IsAny<CancellationToken>()))
             .Returns(ToAsyncEnumerableAsync(testMessages));
+
+        this.Setup(provider => provider.CreateMessageAsync(
+                It.IsAny<string>(),
+                It.IsAny<ChatMessage>(),
+                It.IsAny<CancellationToken>()))
+            .Returns(Task.FromResult(testMessages.First()));
     }
 
     private string CreateConversationId()
diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/ObjectModel/AddConversationMessageExecutorTest.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/ObjectModel/AddConversationMessageExecutorTest.cs
new file mode 100644
index 0000000000..ec0531711d
--- /dev/null
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/ObjectModel/AddConversationMessageExecutorTest.cs
@@ -0,0 +1,83 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.Agents.AI.Workflows.Declarative.Extensions;
+using Microsoft.Agents.AI.Workflows.Declarative.ObjectModel;
+using Microsoft.Bot.ObjectModel;
+using Microsoft.Extensions.AI;
+using Xunit.Abstractions;
+
+namespace Microsoft.Agents.AI.Workflows.Declarative.UnitTests.ObjectModel;
+
+/// <summary>
+/// Tests for <see cref="AddConversationMessageExecutor"/>.
+/// </summary>
+public sealed class AddConversationMessageExecutorTest(ITestOutputHelper output) : WorkflowActionExecutorTest(output)
+{
+    [Theory]
+    [InlineData(AgentMessageRole.User)]
+    [InlineData(AgentMessageRole.Agent)]
+    public async Task AddMessageSuccessfullyAsync(AgentMessageRole role)
+    {
+        // Arrange, Act, Assert
+        await this.ExecuteTestAsync(
+            displayName: nameof(AddMessageSuccessfullyAsync),
+            variableName: "TestMessage",
+            role: AgentMessageRoleWrapper.Get(role),
+            messageText: $"Hello from {role}");
+    }
+
+    private async Task ExecuteTestAsync(
+        string displayName,
+        string variableName,
+        AgentMessageRoleWrapper role,
+        string messageText)
+    {
+        // Arrange
+        MockAgentProvider mockAgentProvider = new();
+        AddConversationMessage model = this.CreateModel(
+            this.FormatDisplayName(displayName),
+            FormatVariablePath(variableName),
+            "TestConversationId",
+            role,
+            messageText);
+
+        AddConversationMessageExecutor action = new(model, mockAgentProvider.Object, this.State);
+
+        // Act
+        await this.ExecuteAsync(action);
+
+        // Assert
+        ChatMessage? testMessage = mockAgentProvider.TestMessages?.FirstOrDefault();
+        Assert.NotNull(testMessage);
+        VerifyModel(model, action);
+        this.VerifyState(variableName, testMessage.ToRecord());
+    }
+
+    private AddConversationMessage CreateModel(
+        string displayName,
+        string messageVariable,
+        string conversationId,
+        AgentMessageRoleWrapper role,
+        string messageText)
+    {
+        AddConversationMessage.Builder actionBuilder =
+            new()
+            {
+                Id = this.CreateActionId(),
+                DisplayName = this.FormatDisplayName(displayName),
+                Message = PropertyPath.Create(messageVariable),
+                ConversationId = StringExpression.Literal(conversationId),
+                Role = role,
+            };
+
+        actionBuilder.Content.Add(new AddConversationMessageContent.Builder
+        {
+            Type = AgentMessageContentType.Text,
+            Value = TemplateLine.Parse(messageText)
+        });
+
+        return AssignParent<AddConversationMessage>(actionBuilder);
+    }
+}