diff --git a/modules/swagger-codegen/src/main/resources/csharp/api_test.mustache b/modules/swagger-codegen/src/main/resources/csharp/api_test.mustache
index f3f1caeaf0a..2f20508f336 100644
--- a/modules/swagger-codegen/src/main/resources/csharp/api_test.mustache
+++ b/modules/swagger-codegen/src/main/resources/csharp/api_test.mustache
@@ -51,8 +51,8 @@ namespace {{packageName}}.Test
         [Test]
         public void {{operationId}}InstanceTest()
         {
-            // test 'IsInstanceOfType' {{classname}}
-            Assert.IsInstanceOfType(typeof({{classname}}), instance, "instance is a {{classname}}");
+            // TODO uncomment below to test 'IsInstanceOfType' {{classname}}
+            //Assert.IsInstanceOfType(typeof({{classname}}), instance, "instance is a {{classname}}");
         }
 
         {{#operations}}{{#operation}}
diff --git a/modules/swagger-codegen/src/main/resources/csharp/packages_test.config.mustache b/modules/swagger-codegen/src/main/resources/csharp/packages_test.config.mustache
index 95192a480bf..7e6f4575391 100644
--- a/modules/swagger-codegen/src/main/resources/csharp/packages_test.config.mustache
+++ b/modules/swagger-codegen/src/main/resources/csharp/packages_test.config.mustache
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
-  <package id="NUnit" version="3.2.1" targetFramework="{{targetFrameworkNuget}}" />
+  <package id="NUnit" version="2.6.4" targetFramework="{{targetFrameworkNuget}}" />
   <package id="RestSharp" version="105.1.0" targetFramework="{{targetFrameworkNuget}}" developmentDependency="true" />
   <package id="Newtonsoft.Json" version="8.0.3" targetFramework="{{targetFrameworkNuget}}" developmentDependency="true" />
 </packages>
diff --git a/samples/client/petstore/csharp/SwaggerClient/IO.Swagger.sln b/samples/client/petstore/csharp/SwaggerClient/IO.Swagger.sln
index c10f905241c..0456bee0d8b 100644
--- a/samples/client/petstore/csharp/SwaggerClient/IO.Swagger.sln
+++ b/samples/client/petstore/csharp/SwaggerClient/IO.Swagger.sln
@@ -2,7 +2,7 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 2012
 VisualStudioVersion = 12.0.0.0
 MinimumVisualStudioVersion = 10.0.0.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IO.Swagger", "src\IO.Swagger\IO.Swagger.csproj", "{4744D957-AA0D-4BF3-A0B6-60A13E6749BB}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IO.Swagger", "src\IO.Swagger\IO.Swagger.csproj", "{ACE32FB1-CE7D-4A06-B9D3-1955C51516CA}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "IO.Swagger.Test", "src\IO.Swagger.Test\IO.Swagger.Test.csproj", "{19F1DEBC-DE5E-4517-8062-F000CD499087}"
 EndProject
@@ -12,10 +12,10 @@ Debug|Any CPU = Debug|Any CPU
 Release|Any CPU = Release|Any CPU
 EndGlobalSection
 GlobalSection(ProjectConfigurationPlatforms) = postSolution
-{4744D957-AA0D-4BF3-A0B6-60A13E6749BB}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-{4744D957-AA0D-4BF3-A0B6-60A13E6749BB}.Debug|Any CPU.Build.0 = Debug|Any CPU
-{4744D957-AA0D-4BF3-A0B6-60A13E6749BB}.Release|Any CPU.ActiveCfg = Release|Any CPU
-{4744D957-AA0D-4BF3-A0B6-60A13E6749BB}.Release|Any CPU.Build.0 = Release|Any CPU
+{ACE32FB1-CE7D-4A06-B9D3-1955C51516CA}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+{ACE32FB1-CE7D-4A06-B9D3-1955C51516CA}.Debug|Any CPU.Build.0 = Debug|Any CPU
+{ACE32FB1-CE7D-4A06-B9D3-1955C51516CA}.Release|Any CPU.ActiveCfg = Release|Any CPU
+{ACE32FB1-CE7D-4A06-B9D3-1955C51516CA}.Release|Any CPU.Build.0 = Release|Any CPU
 {19F1DEBC-DE5E-4517-8062-F000CD499087}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 {19F1DEBC-DE5E-4517-8062-F000CD499087}.Debug|Any CPU.Build.0 = Debug|Any CPU
 {19F1DEBC-DE5E-4517-8062-F000CD499087}.Release|Any CPU.ActiveCfg = Release|Any CPU
diff --git a/samples/client/petstore/csharp/SwaggerClient/README.md b/samples/client/petstore/csharp/SwaggerClient/README.md
index db0560b134f..87ac879ca46 100644
--- a/samples/client/petstore/csharp/SwaggerClient/README.md
+++ b/samples/client/petstore/csharp/SwaggerClient/README.md
@@ -6,7 +6,7 @@ This C# SDK is automatically generated by the [Swagger Codegen](https://github.c
 
 - API version: 1.0.0
 - SDK version: 1.0.0
-- Build date: 2016-07-13T19:06:48.432+08:00
+- Build date: 2016-07-21T17:39:01.768+08:00
 - Build package: class io.swagger.codegen.languages.CSharpClientCodegen
 
 ## Frameworks supported
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger.Test/packages.config b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger.Test/packages.config
index 317248179b6..9bb00f0fc4f 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger.Test/packages.config
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger.Test/packages.config
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
-  <package id="NUnit" version="3.2.1" targetFramework="net45" />
+  <package id="NUnit" version="2.6.4" targetFramework="net45" />
   <package id="RestSharp" version="105.1.0" targetFramework="net45" developmentDependency="true" />
   <package id="Newtonsoft.Json" version="8.0.3" targetFramework="net45" developmentDependency="true" />
 </packages>
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Client/Configuration.cs b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Client/Configuration.cs
index 60a2adac79a..fcefd40a36c 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Client/Configuration.cs
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Client/Configuration.cs
@@ -179,9 +179,36 @@ namespace IO.Swagger.Client
         /// <returns></returns>
         public void AddDefaultHeader(string key, string value)
         {
+            if (_defaultHeaderMap.ContainsKey(key))
+                _defaultHeaderMap.Remove(key);
             _defaultHeaderMap.Add(key, value);
         }
 
+        /// <summary>
+        /// Add Api Key Header.
+        /// </summary>
+        /// <param name="key">Api Key name.</param>
+        /// <param name="value">Api Key value.</param>
+        /// <returns></returns>
+        public void AddApiKey(string key, string value)
+        {
+            if (ApiKey.ContainsKey(key))
+                ApiKey.Remove(key);
+            ApiKey.Add(key, value);
+        }
+
+        /// <summary>
+        /// Sets the API key prefix.
+        /// </summary>
+        /// <param name="key">Api Key name.</param>
+        /// <param name="value">Api Key value.</param>
+        public void AddApiKeyPrefix(string key, string value)
+        {
+            if (ApiKeyPrefix.ContainsKey(key))
+                ApiKeyPrefix.Remove(key);
+            ApiKeyPrefix.Add(key, value);
+        }
+
         /// <summary>
         /// Gets or sets the HTTP user agent.
         /// </summary>
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/IO.Swagger.csproj b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/IO.Swagger.csproj
index e03d788d32d..d46a58703fd 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/IO.Swagger.csproj
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/IO.Swagger.csproj
@@ -24,7 +24,7 @@ limitations under the License.
   <PropertyGroup>
     <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
     <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
-    <ProjectGuid>{4744D957-AA0D-4BF3-A0B6-60A13E6749BB}</ProjectGuid>
+    <ProjectGuid>{ACE32FB1-CE7D-4A06-B9D3-1955C51516CA}</ProjectGuid>
     <OutputType>Library</OutputType>
     <AppDesignerFolder>Properties</AppDesignerFolder>
     <RootNamespace>Swagger Library</RootNamespace>