Document workflow edge test helpers

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Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>

dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs

@@ -116,6 +116,13 @@ public static class WorkflowBuilderExtensions
         static bool IsAllowedType(object? message) => message is null;
     }
 
+    /// <summary>
+    /// Validates a target collection and returns it as a list.
+    /// </summary>
+    /// <param name="targets">The target executor bindings to validate.</param>
+    /// <returns>A validated list of target executor bindings.</returns>
+    /// <exception cref="ArgumentNullException">Thrown when <paramref name="targets"/> is null or contains a null element.</exception>
+    /// <exception cref="ArgumentException">Thrown when <paramref name="targets"/> is empty.</exception>
     private static List<ExecutorBinding> ValidateTargets(IEnumerable<ExecutorBinding> targets)
     {
         Throw.IfNull(targets);

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

@@ -447,6 +447,9 @@ public partial class WorkflowBuilderSmokeTests
         Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.WithDefault([target, null!]));
     }
 
+    /// <summary>
+    /// Gets the only edge emitted by the specified workflow source.
+    /// </summary>
     private static Edge GetSingleEdge(Workflow workflow, string sourceId)
         => workflow.Edges[sourceId].Should().ContainSingle().Subject;
 }