OpenSTA is a free, open source, HTTP/S load, stress, and performance testing tool with features rivaling many commercial load-testing tools. When load testing Microsoft .NET applications with OpenSTA, one of the first issues that the script developer encounters is managing the ViewState parameter. This article details a solution for capturing and replaying with the .NET ViewState parameter using OpenSTA. It also discusses practical performance tuning issues associated with .NET and using "ViewState."
Load, Stress, and Performance Testing with OpenSTA
Taming the Microsoft .NET ViewState with SCL