This contribution is an experience report on system testing and in particular on the testing of a datawarehouse system. Datawarehouses are large databases used solely for querying and reporting purposes. The datawarehouse in question here was dedicated to fulfilling the reporting requirements of the BASEL-II agreement on the provision of auditing data by the banks, the European equivalent of the Sarbane-Oxley Act. The purpose of the testing project was to prove that the contents of the datawarehouse are correct in accordance with the rules specified to fill them. In the end, the only way to achieve this was to rewrite the rule specifications in a machine readable form and to transform them into post assertions, which could be interpreted by a data verification tool for comparison of the actual data contents with the expected data contents. The testing project was never fully completed, since not all of the rules could be properly transformed. Keywords: System Testing, Datawarehouse Testing, Data Transformation Rules, Post Conditions Assertions, Formal Verification.