Remove reflection from Connect test

This removes the reflection from the double connection test and replaces it with a
`MockHttpHandler` to let the connection actually succeed and then test the
redundant `ConnectAsync` call.

partial fix for #48

Author: jaredpar

tests/ModelContextProtocol.Tests/Transport/SseClientTransportTests.cs

@@ -5,6 +5,7 @@
 using ModelContextProtocol.Tests.Utils;
 using System.Net;
 using System.Reflection;
+using System.Reflection.Metadata;
 
 namespace ModelContextProtocol.Tests.Transport;
 
@@ -107,12 +108,53 @@ public async Task ConnectAsync_Should_Connect_Successfully()
     [Fact]
     public async Task ConnectAsync_Throws_If_Already_Connected()
     {
-        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, NullLoggerFactory.Instance);
-        transport.GetType().BaseType!.GetField("_isConnected", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)?.SetValue(transport, true);
+        using var mockHttpHandler = new MockHttpHandler();
+        using var httpClient = new HttpClient(mockHttpHandler);
+        await using var transport = new SseClientTransport(_transportOptions, _serverConfig, httpClient, NullLoggerFactory.Instance);
+        using var mreConnected = new ManualResetEventSlim(false);
+        using var mreDone = new ManualResetEventSlim(false);
+        var callIndex = 0;
+
+        mockHttpHandler.RequestHandler = (request) =>
+        {
+            switch (callIndex++)
+            {
+                case 0:
+                    return Task.FromResult(new HttpResponseMessage
+                    {
+                        StatusCode = HttpStatusCode.OK,
+                        Content = new StringContent("event: endpoint\r\ndata: http://localhost\r\n\r\n")
+                    });
+                case 1:
+                    mreConnected.Set();
+                    mreDone.Wait();
+                    return Task.FromResult(new HttpResponseMessage
+                    {
+                        StatusCode = HttpStatusCode.OK,
+                        Content = new StringContent("")
+                    });
+                default:
+                    return Task.FromResult(new HttpResponseMessage
+                    {
+                        StatusCode = HttpStatusCode.OK,
+                        Content = new StringContent("")
+                    });
+            }
+        };
 
+        var task = Task.Run(async () =>
+        {
+            await transport.ConnectAsync(TestContext.Current.CancellationToken);
+        }, TestContext.Current.CancellationToken);
+
+        mreConnected.Wait(TestContext.Current.CancellationToken);
+        Assert.True(transport.IsConnected);
         var action = async () => await transport.ConnectAsync();
         var exception = await Assert.ThrowsAsync<McpTransportException>(action);
         Assert.Equal("Transport is already connected", exception.Message);
+        mreDone.Set();
+        await transport.CloseAsync();
+        await task;
     }
 
     [Fact]