There are several techniques that have been created to load test WCF Services. These include commercial and open source tools like WCF Load Test available on CodePlex. I have seen several packages over the past few years to perform load testing on web pages and web services including the load testing tools built into Visual Studio. Some were easy to setup, others not so much. WCF Services are unique from a plain old web page because of message payloads, security requirements and multiple protocol support.
Testing services, any code for that matter, is crucial to having reliable software. Load testing helps you flesh out bugs that would not ordinarily surface in unit or integration tests. It is also important to load test services utilizing more real-world demand patterns, not just linear.
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