Greetings,
I've found that WCAT does not handle cookies in a predictable manner. For example, when a WCAT client is pointed at either an IIS (.net) or Apache (.php) environment I've found that each request is often treated as a unique session since the expected cookies are not appearing in the request headers (verified using a network monitoring application).
In comparison, manual requests to the same environments using a browser (such as IE or Firefox) result in cookies being included as expected. Also, other load/stress testing tools, such as the legacy Microsoft Web Application Stress Tool (WAST), JMeter, etc... correctly handle the cookies for the same target sites as expected. Again, these findings were verified using a network monitoring tool to inspect the request headers.
In addition, I tested the cookie issue against a few third party sites (and kept the load level very low out of consideration). Same type of issues occurred.
So far, cookie handling by WCAT has been successful on only one of our test environments. Given this, I suspect that there is something about the way WCAT makes a request that prevents a server from issuing a cookie....or WCAT fails to set cookies issued by environments with certain configurations.
Either way, it limits the usefulness of the WCAT tool, since a persistent session is often required for many stress test scenarios (such as those involving a login/logout).
Initially, I thought this was only an issue with Apache, but I have since reproduced the problem on IIS 6 environments as well. That's why I'm posting in this section now.
My complete notes, including WCAT client script, can be found at the following (original) post:
http://forums.iis.net/p/1162115/1922515.aspx#1922515
...Dirk