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How to: Create a Load Test Plug-In

You can create a load test plug-in to run code at different times while the load test is running. You create a plug-in to expand upon or modify the built in functionality of the load test. For example, you can code a load test plug-in to set or modify the load test pattern while the load test is running. To do this, you must create a class that inherits the ILoadTestPlugin interface. This class must implement the Initialize method of this interface. For more information, see ILoadTestPlugin.


You can also create plug-ins for Web performance tests. For more information, see How to: Create a Web Performance Test Plug-In


  • Visual Studio Ultimate

To create a Load Test Plug-in by using Visual C#

  1. Open a Web performance and load test project that contains a Web performance test.

    For more information, see How to: Create and Configure Test Projects for Automated Tests.

  2. Add a load test to the test project and configure it to run a Web performance test.

    For more information, see [retired] Creating load tests.

  3. In Solution Explorer, right-click on the solution and select Add and then choose New Project.

    The Add New Project dialog box is displayed.

  4. Under Installed Templates, select Visual C#.

  5. In the list of templates, select Class Library.

  6. In the Name text box, type a name for your class.

  7. Choose OK.

  8. The new class library project is added to Solution Explorer and the new class appears in the Code Editor.

  9. In Solution Explorer, right-click the References folder in the new class library and select Add Reference.

  10. The Add Reference dialog box is displayed.

  11. Choose the .NET tab, scroll down, and then select Microsoft.VisualStudio.QualityTools.LoadTestFramework.

  12. Choose OK.

    The reference to Microsoft.VisualStudio.QualityTools.LoadTestFramework is added to the Reference folder in Solution Explorer.

  13. In Solution Explorer, right-click the top node of the Web performance and load test project that contains the load test to which you want to add the load test plug-in and select Add Reference.

  14. The Add Reference dialog box is displayed.

  15. Choose the Projects tab and select the Class Library Project.

  16. Choose OK.

  17. In the Code Editor, add a using statement for the Microsoft.VisualStudio.TestTools.LoadTesting namespace.

  18. Implement the ILoadTestPlugin interface for the class that was created in the Class Library project. See the following Example section for a sample implementation.

  19. After you have written the code, build the new project.

  20. Right-click on the top node of the load test and then choose Add Load Test Plug-in.

    The Add Load Test Plug-in dialog box is displayed.

  21. Under Select a plug-in, select your load test plug-in class.

  22. In the Properties for selected plug-in pane, set the initial values for the plug-in to use at run time.


    You can expose as many properties as you want from your plug-ins; just make them public, settable, and of a base type such as Integer, Boolean, or String. You can also change the Web performance test plug-in properties later by using the Properties window.

  23. Choose OK.

    The plug-in is added to the Load Test Plug-ins folder.


    You might get an error similar to the following when you run a Web performance test or load test that uses your plug-in:

    Request failed: Exception in <plug-in> event: Could not load file or assembly '<"Plug-in name".dll file>, Version=<n.n.n.n>, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.

    This is caused if you make code changes to any of your plug-ins and create a new DLL version (Version=, but the plug-in is still referencing the original plug-in version. To correct this problem, follow these steps:

    1. In your Web performance and load test project, you will see a warning in references. Remove and re-add the reference to your plug-in DLL.

    2. Remove the plug-in from your test or the appropriate location and then add it back.


The following code shows a load test plug-in that runs custom code after a LoadTestFinished event occurs. If this code is run on a test agent on a remote machine and the test agent does not have a localhost SMTP service, the load test will remain in the "In progress" state because a message box will be open.


The following code requires that you add a reference to System.Windows.Forms.

using System;
using Microsoft.VisualStudio.TestTools.LoadTesting;
using System.Net.Mail;
using System.Windows.Forms;

namespace LoadTestPluginTest
    public class MyLoadTestPlugin : ILoadTestPlugin
        LoadTest myLoadTest;

        public void Initialize(LoadTest loadTest)
            myLoadTest = loadTest;
            myLoadTest.LoadTestFinished += new

        void myLoadTest_LoadTestFinished(object sender, EventArgs e)
                // place custom code here
                MailAddress MyAddress = new MailAddress("");
                MailMessage MyMail = new MailMessage(MyAddress, MyAddress);
                MyMail.Subject = "Load Test Finished -- Admin Email";
                MyMail.Body = myLoadTest..Name + " has finished.";

                SmtpClient MySmtpClient = new SmtpClient("localhost");

            catch (SmtpException ex)
                MessageBox.Show(ex.InnerException.Message +
                    ".\r\nMake sure you have a valid SMTP.", "LoadTestPlugin", MessageBoxButtons.OK, MessageBoxIcon.Warning, MessageBoxDefaultButton.Button1);

Eight events are associated with a load test that can be handled in the load test plug-in to run custom code with the load test. The following is a list of the events that provide access to different periods of the load test run:

See Also


How to: Create a Web Performance Test Plug-In



Other Resources

Create custom code and plug-ins for load tests