The paper describes the preparation and execution of the site acceptance testing of a large scale industrial system. A use case based approach to testing is developed. The approach introduces three-level test artifact specifications. At the highest level test scenarios are used to validate system use cases. The lower levels are presented by test scripts and test cases, which unfold test scenarios into test procedures with corresponding test data. A proposed requirements traceability model joins all the test artifacts to each other and to the requirements allowing testers to maintain control over requirements coverage during the entire testing process. The paper also describes successful practical experience in application of the approach as well as our observations regarding usage of modern testing techniques and tools in industry.