[Python] Add echo_api test object serialization for multipart requests (#18176)

* [python] echo add test object serialization for multipart requests

* [echo api] update samples

* [echo api] update samples

samples/client/echo_api/csharp-restsharp/src/Org.OpenAPITools.Test/Model/TestFormObjectMultipartRequestMarkerTests.cs

@@ -0,0 +1,67 @@
+/*
+ * Echo Server API
+ *
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ * Generated by: https://github.com/openapitools/openapi-generator.git
+ */
+
+
+using Xunit;
+
+using System;
+using System.Linq;
+using System.IO;
+using System.Collections.Generic;
+using Org.OpenAPITools.Model;
+using Org.OpenAPITools.Client;
+using System.Reflection;
+using Newtonsoft.Json;
+
+namespace Org.OpenAPITools.Test.Model
+{
+    /// <summary>
+    ///  Class for testing TestFormObjectMultipartRequestMarker
+    /// </summary>
+    /// <remarks>
+    /// This file is automatically generated by OpenAPI Generator (https://openapi-generator.tech).
+    /// Please update the test case below to test the model.
+    /// </remarks>
+    public class TestFormObjectMultipartRequestMarkerTests : IDisposable
+    {
+        // TODO uncomment below to declare an instance variable for TestFormObjectMultipartRequestMarker
+        //private TestFormObjectMultipartRequestMarker instance;
+
+        public TestFormObjectMultipartRequestMarkerTests()
+        {
+            // TODO uncomment below to create an instance of TestFormObjectMultipartRequestMarker
+            //instance = new TestFormObjectMultipartRequestMarker();
+        }
+
+        public void Dispose()
+        {
+            // Cleanup when everything is done.
+        }
+
+        /// <summary>
+        /// Test an instance of TestFormObjectMultipartRequestMarker
+        /// </summary>
+        [Fact]
+        public void TestFormObjectMultipartRequestMarkerInstanceTest()
+        {
+            // TODO uncomment below to test "IsType" TestFormObjectMultipartRequestMarker
+            //Assert.IsType<TestFormObjectMultipartRequestMarker>(instance);
+        }
+
+        /// <summary>
+        /// Test the property 'Name'
+        /// </summary>
+        [Fact]
+        public void NameTest()
+        {
+            // TODO unit test for the property 'Name'
+        }
+    }
+}