.NET: Add tests for subworkflow shared state behavior (#3444)

Adds tests documenting current shared state behavior in subworkflows:

- State works correctly within a subworkflow

- State is isolated across parent/subworkflow boundaries

Related to #2419

dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/Sample/14_Subworkflow_SharedState.cs

@@ -0,0 +1,158 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.Agents.AI.Workflows.Sample;
+
+/// <summary>
+/// Tests for shared state preservation across subworkflow boundaries.
+/// Validates fix for issue #2419: ".NET: Shared State is not preserved in Subworkflows"
+/// </summary>
+internal static class Step14EntryPoint
+{
+    public const string WordStateScope = "WordStateScope";
+
+    /// <summary>
+    /// Tests that shared state works WITHIN a subworkflow (internal persistence).
+    /// This tests whether state written by one executor in a subworkflow can be
+    /// read by another executor in the SAME subworkflow.
+    /// </summary>
+    public static async ValueTask<int> RunSubworkflowInternalStateAsync(string text, TextWriter writer, IWorkflowExecutionEnvironment environment)
+    {
+        // All three executors are INSIDE the subworkflow
+        TextReadExecutor textRead = new();
+        TextTrimExecutor textTrim = new();
+        CharCountingExecutor charCount = new();
+
+        Workflow subWorkflow = new WorkflowBuilder(textRead)
+            .AddEdge(textRead, textTrim)
+            .AddEdge(textTrim, charCount)
+            .WithOutputFrom(charCount)
+            .Build();
+
+        ExecutorBinding subWorkflowStep = subWorkflow.BindAsExecutor("internalStateSubworkflow");
+
+        // Parent workflow just wraps the subworkflow
+        Workflow workflow = new WorkflowBuilder(subWorkflowStep)
+            .WithOutputFrom(subWorkflowStep)
+            .Build();
+
+        await using Run run = await environment.RunAsync(workflow, text);
+
+        int? result = null;
+        foreach (WorkflowEvent evt in run.OutgoingEvents)
+        {
+            if (evt is WorkflowOutputEvent outputEvent)
+            {
+                result = outputEvent.As<int>();
+                writer.WriteLine($"Subworkflow internal state result: {result}");
+            }
+            else if (evt is WorkflowErrorEvent failedEvent)
+            {
+                writer.WriteLine($"Workflow failed: {failedEvent.Data}");
+                throw failedEvent.Data as Exception ?? new InvalidOperationException(failedEvent.Data?.ToString());
+            }
+        }
+
+        return result ?? throw new InvalidOperationException("No output produced");
+    }
+
+    /// <summary>
+    /// Tests cross-boundary state behavior (parent → subworkflow → parent).
+    /// This documents the current behavior for issue #2419: state is isolated across subworkflow boundaries.
+    /// </summary>
+    public static async ValueTask<Exception?> RunCrossBoundaryStateAsync(string text, TextWriter writer, IWorkflowExecutionEnvironment environment)
+    {
+        TextReadExecutor textRead = new();
+        TextTrimExecutor textTrim = new();
+        CharCountingExecutor charCount = new();
+
+        // Create a subworkflow containing just the trim executor
+        Workflow subWorkflow = new WorkflowBuilder(textTrim)
+            .WithOutputFrom(textTrim)
+            .Build();
+
+        ExecutorBinding subWorkflowStep = subWorkflow.BindAsExecutor("textTrimSubworkflow");
+
+        // Create the main workflow: parent → subworkflow → parent
+        Workflow workflow = new WorkflowBuilder(textRead)
+            .AddEdge(textRead, subWorkflowStep)
+            .AddEdge(subWorkflowStep, charCount)
+            .WithOutputFrom(charCount)
+            .Build();
+
+        await using Run run = await environment.RunAsync(workflow, text);
+
+        foreach (WorkflowEvent evt in run.OutgoingEvents)
+        {
+            if (evt is WorkflowOutputEvent outputEvent)
+            {
+                writer.WriteLine($"Cross-boundary state result: {outputEvent.As<int>()}");
+                return null; // Success - no error
+            }
+            else if (evt is WorkflowErrorEvent failedEvent)
+            {
+                writer.WriteLine($"Workflow failed: {failedEvent.Data}");
+                return failedEvent.Data as Exception;
+            }
+        }
+
+        return new InvalidOperationException("No output produced");
+    }
+
+    /// <summary>
+    /// Executor that reads text and stores it in shared state with a generated key.
+    /// </summary>
+    internal sealed class TextReadExecutor() : Executor("TextReadExecutor")
+    {
+        protected override RouteBuilder ConfigureRoutes(RouteBuilder routeBuilder)
+            => routeBuilder.AddHandler<string, string>(this.HandleAsync);
+
+        private async ValueTask<string> HandleAsync(string text, IWorkflowContext context, CancellationToken cancellationToken = default)
+        {
+            string key = Guid.NewGuid().ToString();
+            await context.QueueStateUpdateAsync(key, text, scopeName: WordStateScope, cancellationToken);
+            return key;
+        }
+    }
+
+    /// <summary>
+    /// Executor that reads text from shared state, trims it, and updates the state.
+    /// </summary>
+    internal sealed class TextTrimExecutor() : Executor("TextTrimExecutor")
+    {
+        protected override RouteBuilder ConfigureRoutes(RouteBuilder routeBuilder)
+            => routeBuilder.AddHandler<string, string>(this.HandleAsync);
+
+        private async ValueTask<string> HandleAsync(string key, IWorkflowContext context, CancellationToken cancellationToken = default)
+        {
+            string? content = await context.ReadStateAsync<string>(key, scopeName: WordStateScope, cancellationToken);
+            if (content is null)
+            {
+                throw new InvalidOperationException($"Word state not found for key: {key}");
+            }
+
+            string trimmed = content.Trim();
+            await context.QueueStateUpdateAsync(key, trimmed, scopeName: WordStateScope, cancellationToken);
+            return key;
+        }
+    }
+
+    /// <summary>
+    /// Executor that reads text from shared state and returns its character count.
+    /// </summary>
+    internal sealed class CharCountingExecutor() : Executor("CharCountingExecutor")
+    {
+        protected override RouteBuilder ConfigureRoutes(RouteBuilder routeBuilder)
+            => routeBuilder.AddHandler<string, int>(this.HandleAsync);
+
+        private async ValueTask<int> HandleAsync(string key, IWorkflowContext context, CancellationToken cancellationToken = default)
+        {
+            string? content = await context.ReadStateAsync<string>(key, scopeName: WordStateScope, cancellationToken);
+            return content?.Length ?? 0;
+        }
+    }
+}

dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/SampleSmokeTest.cs

@@ -437,6 +437,58 @@ public class SampleSmokeTest
             );
         }
     }
+
+    /// <summary>
+    /// Tests that shared state works WITHIN a subworkflow (internal persistence).
+    /// This verifies state written by one executor in a subworkflow can be read
+    /// by another executor in the SAME subworkflow.
+    /// </summary>
+    [Theory]
+    [InlineData(ExecutionEnvironment.InProcess_Lockstep)]
+    [InlineData(ExecutionEnvironment.InProcess_OffThread)]
+    internal async Task Test_RunSample_Step14_SharedState_WorksWithinSubworkflowAsync(ExecutionEnvironment environment)
+    {
+        // Arrange
+        IWorkflowExecutionEnvironment executionEnvironment = environment.ToWorkflowExecutionEnvironment();
+        const string Text = "    Lorem ipsum dolor sit amet, consectetur adipiscing elit.  ";
+        int expectedCharCount = Text.Trim().Length;
+
+        // Act & Assert - All executors inside the subworkflow should share state
+        using StringWriter writer = new();
+        int result = await Step14EntryPoint.RunSubworkflowInternalStateAsync(Text, writer, executionEnvironment);
+        result.Should().Be(expectedCharCount, "executors within subworkflow should share state correctly");
+    }
+
+    /// <summary>
+    /// Documents that shared state is currently isolated across subworkflow boundaries.
+    /// This is the behavior reported in issue #2419.
+    /// When/if cross-boundary state sharing is implemented, this test should be updated
+    /// to expect success instead of failure.
+    /// </summary>
+    [Theory]
+    [InlineData(ExecutionEnvironment.InProcess_Lockstep)]
+    [InlineData(ExecutionEnvironment.InProcess_OffThread)]
+    internal async Task Test_RunSample_Step14a_SharedState_IsolatedAcrossSubworkflowBoundaryAsync(ExecutionEnvironment environment)
+    {
+        // Arrange
+        IWorkflowExecutionEnvironment executionEnvironment = environment.ToWorkflowExecutionEnvironment();
+        const string Text = "    Lorem ipsum dolor sit amet, consectetur adipiscing elit.  ";
+
+        // Act - Attempt to use shared state across parent/subworkflow boundary
+        using StringWriter writer = new();
+        Exception? error = await Step14EntryPoint.RunCrossBoundaryStateAsync(Text, writer, executionEnvironment);
+
+        // Assert - Currently, state is isolated across subworkflow boundaries (issue #2419)
+        // The subworkflow executor cannot see state written by the parent workflow
+        error.Should().NotBeNull("state written in parent workflow is not visible in subworkflow");
+
+        // The exception may be wrapped in TargetInvocationException, so check inner exception too
+        Exception actualError = error is System.Reflection.TargetInvocationException tie && tie.InnerException != null
+            ? tie.InnerException
+            : error;
+
+        actualError.Should().BeOfType<InvalidOperationException>();
+    }
 }
 
 internal sealed class VerifyingPlaybackResponder<TInput, TResponse>