User modeling in VSTS Load Tests

A common question we are asked is how we deal with "new" vs. "return" users in a load test. Web browsers cache content and store cookies, which impacts the pattern and content of requests that are sent to the web server.

Load test scenarios have a "Percentage of new users" property that you can use to control this.

When a load test starts, the load test engine creates a queue of user profiles the size of the maximum load in the load test.

When a new vuser is started due to an increase in load, we use a random number and the "Percentage of new users" property to determine if the user is a "new user" or a "return user". New users have an empty cache and no cookies. Return users' cache and cookie store are built up as the test runs. If the user is a return user, the user is picked off the user queue, and the user's cookie and browser cache are used in the web test.

Each user has a unique id, which is available in the web test WebTest.Context.WebTestUserId property. A user's cookie collection is available in the WebTest.Context.CookieContainer property. Unfortunately we do not give programmatic access to the browser cache in the same way. The WebTest.Context.IsNewUser property does indicates if a user is a new user or return user.

User id's are scoped per agent, so each agent uses the same set of user ids. The unique agent id is in the WebTest.Context.AgentId property.

Ed.

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