Add asserts to test

Author: stephentoub

tests/ModelContextProtocol.Tests/Transport/StdioClientTransportTests.cs

@@ -1,6 +1,7 @@
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Tests.Utils;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace ModelContextProtocol.Tests.Transport;
 
@@ -25,7 +26,16 @@ public async Task CreateAsync_ValidProcessInvalidServer_StdErrCallbackInvoked()
         string id = Guid.NewGuid().ToString("N");
 
         int count = 0;
-        Action<string> stdErrCallback = line => Interlocked.Increment(ref count);
+        StringBuilder sb = new();
+        Action<string> stdErrCallback = line =>
+        {
+            Assert.NotNull(line);
+            lock (sb)
+            {
+                sb.AppendLine(line);
+                count++;
+            }
+        };
 
         StdioClientTransport transport = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ?
             new(new() { Command = "cmd", Arguments = ["/C", $"echo \"{id}\" >&2"], StandardErrorLines = stdErrCallback }, LoggerFactory) :
@@ -34,5 +44,6 @@ public async Task CreateAsync_ValidProcessInvalidServer_StdErrCallbackInvoked()
         await Assert.ThrowsAsync<IOException>(() => McpClientFactory.CreateAsync(transport, loggerFactory: LoggerFactory, cancellationToken: TestContext.Current.CancellationToken));
 
         Assert.InRange(count, 1, int.MaxValue);
+        Assert.Contains(id, sb.ToString());
     }
 }