Fix private reflection (#60)

* Fix private reflection

Two changes in this PR

- Remove private reflection from one of the tests
- Move to use `TaskCompletionSource` (feedback from previous PR)

* fix

* spelling

tests/ModelContextProtocol.Tests/Server/McpServerTests.cs

@@ -89,10 +89,12 @@ public class McpServerTests
     {
         // Arrange
         await using var server = McpServerFactory.Create(_serverTransport.Object, _options, _loggerFactory.Object, _serviceProvider);
-        server.GetType().GetField("_isInitializing", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)?.SetValue(server, true);
+        var task = server.StartAsync(TestContext.Current.CancellationToken);
 
         // Act & Assert
         await Assert.ThrowsAsync<InvalidOperationException>(() => server.StartAsync(TestContext.Current.CancellationToken));
+
+        await task;
     }
 
     [Fact]